SharePoint

SharePoint is a web-based collaborative platform that integrates with Microsoft Office. Launched in 2001, SharePoint is primarily sold as a document management and storage system, but the product is highly configurable and usage varies substantially among organizations.
Microsoft states that SharePoint has 190 million users across 200,000 customer organizations.
Editions.
There are various editions of SharePoint which have different functions.
SharePoint Server.
SharePoint Server is provided to organizations that seek greater control over SharePoint's behavior or design. This product is installed on customers' IT infrastructure. It receives fewer frequent updates but has access to a wider set of features and customization capabilities. There are two editions of SharePoint Server: Standard and Enterprise. A free version called 'Foundation' was discontinued in 2016. These servers may be provisioned as normal virtual/cloud servers or as hosted services.
SharePoint Standard.
Microsoft SharePoint Standard builds on the Microsoft SharePoint Foundation in a few key product areas-
SharePoint Standard licensing includes a CAL (client access license) component and a server fee. SharePoint Standard may also be licensed through a cloud model.
SharePoint Enterprise.
Built upon SharePoint Standard, Microsoft SharePoint Enterprise features can be unlocked by providing an additional license key.
Extra features in SharePoint Enterprise include:
SharePoint Enterprise licensing includes a CAL component and a server fee that must be purchased "in addition to" SharePoint Server licensing. SharePoint Enterprise may also be licensed through a cloud model.
SharePoint Online.
Microsoft's hosted SharePoint is typically bundled in Microsoft 365 subscriptions, but can be licensed separately. SharePoint Online has the advantage of not needing to maintain one's own servers, but as a result lacks the customization options of a self-hosted installation of SharePoint.
It is limited to a core set of collaboration, file hosting, and document and content management scenarios, and is updated on a frequent basis, but is typically comparable with SharePoint Enterprise. 
Currently, additional capabilities include:
Missing capabilities include:
Microsoft lists changes in SharePoint Online on its Office Roadmap.
Applications.
SharePoint usage varies from organization to organization. The product encompasses a wide variety of capabilities, most of which require configuration and governance.
The most common uses of the SharePoint include:
Enterprise content and document management.
SharePoint allows for storage, retrieval, searching, archiving, tracking, management, and reporting on electronic documents and records. Many of the functions in this product are designed around various legal, information management, and process requirements in organizations. SharePoint also provides search and 'graph' functionality. SharePoint's integration with Microsoft Windows and Microsoft Office allow for collaborative real-time editing, and encrypted/information rights managed synchronization.
This capability is often used to replace an existing corporate file server, and is typically coupled with an enterprise content management policy.
Intranet and social network.
A SharePoint intranet or intranet portal is a way to centralize access to enterprise information and applications. It is a tool that helps an organization manage its internal communications, applications and information more easily. Microsoft claims that this has organizational benefits such as increased employee engagement, centralizing process management, reducing new staff on-boarding costs, and providing the means to capture and share tacit knowledge (e.g. via tools such as wikis).
Collaborative software.
SharePoint contains team collaboration groupware capabilities, including: project scheduling (integrated with Outlook and Project), social collaboration, shared mailboxes, and project related document storage and collaboration. Groupware in SharePoint is based around the concept of a "Team Site".
File hosting service (personal cloud).
SharePoint Server hosts OneDrive for Business, which allows storage and synchronization of an individual's personal documents, as well as public/private file sharing of those documents. This is typically combined with other Microsoft Office Servers/Services, such as Microsoft Exchange, to produce a "personal cloud",
WebDAV can be used to access files without using the web interface. However, Microsoft's implementation of WebDAV doesn't conform to the official WebDAV protocol and therefore isn't compliant to the WebDAV standard. For example, WebDAV applications have to support the language tagging functionality of the XML specification which Microsoft's implementation doesn't. Only Windows XP to Windows 8 are supported.
Custom web applications.
SharePoint's custom development capabilities provide an additional layer of services that allow rapid prototyping of integrated (typically line-of-business) web applications. SharePoint provides developers with integration into corporate directories and data sources through standards such as REST/OData/OAuth. Enterprise application developers use SharePoint's security and information management capabilities across a variety of development platforms and scenarios. SharePoint also contains an enterprise "app store" that has different types of external applications which are encapsulated and managed to access to resources such as corporate user data and document data.
Content structure.
Pages.
SharePoint provides free-form pages which may be edited in-browser. These may be used to provide content to users, or to provide structure to the SharePoint environment.
Web parts and app parts.
Web parts and app parts are components (also known as portlets) that can be inserted into Pages. They are used to display information from both SharePoint and third party applications.
Content item, Content Type, Libraries, Lists, and "Apps".
In SharePoint 2013, in some locations, Lists and Libraries were renamed 'Apps' (despite being unrelated to the "SharePoint App Store"). In SharePoint 2016, some of these were renamed back to Lists and Libraries.
Sites.
A SharePoint Site is a collection of pages, lists, libraries, apps, configurations, features, content types, and sub-sites. Examples of Site templates in SharePoint include: collaboration (team) sites, wiki sites, blank sites, and publishing sites.
Configuration and customization.
Web-based configuration.
SharePoint is primarily configured through a web browser. The web-based user interface provides most of the configuration capability of the product.
Depending on your permission level, the web interface can be used to:
SharePoint Designer.
SharePoint Designer is a semi-deprecated product that provided 'advanced editing' capabilities for HTML/ASPX pages, but remains the primary method of editing SharePoint workflows.
A significant subset of HTML editing features were removed in Designer 2013, and the product is expected to be deprecated in 2016–7.
Microsoft SharePoint's Server Features are configured either using PowerShell, or a Web UI called "Central Administration". Configuration of server farm settings (e.g. search crawl, web application services) can be handled through these central tools.
While Central Administration is limited to farm-wide settings (config DB), it provides access to tools such as the 'SharePoint Health Analyzer', a diagnostic health-checking tool.
In addition to PowerShell's farm configuration features, some limited tools are made available for administering or adjusting settings for sites or site collections in content databases.
A limited subset of these features are available by SharePoint's SaaS providers, including Microsoft.
Custom development.
Customization may appear through:
Server architecture.
SharePoint Server can be scaled down to operate entirely from one developer machine, or scaled up to be managed across hundreds of machines.
Farms.
A SharePoint farm is a logical grouping of SharePoint servers that share common resources. A farm typically operates stand-alone, but can also subscribe to functions from another farm, or provide functions to another farm. Each farm has its own central configuration database, which is managed through either a PowerShell interface, or a Central Administration website (which relies partly on PowerShell's infrastructure). Each server in the farm is able to directly interface with the central configuration database. Servers use this to configure services (e.g. IIS, windows features, database connections) to match the requirements of the farm, and to report server health issues, resource allocation issues, etc...
Web applications.
Web applications (WAs) are top-level containers for content in a SharePoint farm. A web application is associated primarily with IIS configuration. A web application consists of a set of access mappings or URLs defined in the SharePoint central management console, which are replicated by SharePoint across every IIS Instance (e.g. Web Application Servers) configured in the farm.
Site collections.
A site collection is a hierarchical group of 'SharePoint Sites'. Each web application must have at least one site collection. Site collections share common properties (detailed here), common subscriptions to service applications, and can be configured with unique host names. A site collection may have a distinct content databases, or may share a content database with other site collections in the same web application.
Service applications.
Service applications provide granular pieces of SharePoint functionality to other web and service applications in the farm. Examples of service applications include the User Profile Sync service, and the Search Indexing service. A service application can be turned off, exist on one server, or be load-balanced across many servers in a farm. Service Applications are designed to have independent functionality and independent security scopes.
Administration, security, compliance.
SharePoint's architecture enables a 'least-privileges' execution permission model.
SharePoint Central Administration (the CA) is a web application that typically exists on a single server in the farm; however, it is also able to be deployed for redundancy to multiple servers. This application provides a complete centralized management interface for web & service applications in the SharePoint farm, including AD account management for web & service applications. In the event of the failure of the CA, Windows PowerShell is typically used on the CA server to reconfigure the farm.
The structure of the SharePoint platform enables multiple WAs to exist on a single farm. In a shared (cloud) hosting environment, owners of these WAs may require their own management console. The SharePoint 'Tenant Administration' (TA) is an optional web application used by web application owners to manage how their web application interacts with the shared resources in the farm.
History.
Origins.
SharePoint evolved from projects codenamed "Office Server" and "Tahoe" during the Office XP development cycle.
"Office Server" evolved out of the FrontPage and Office Server Extensions and "Team Pages". It targeted simple, bottom-up collaboration.
"Tahoe", built on shared technology with Exchange and the "Digital Dashboard", targeted top-down portals, search and document management. The searching and indexing capabilities of SharePoint came from the "Tahoe" feature set. The search and indexing features were a combination of the index and crawling features from the Microsoft Site Server family of products and from the query language of Microsoft Index Server.
GAC-(Global Assembly Cache) is used to accommodate the shared assemblies that are specifically designated to be shared by applications executed on a system.
Versions.
Successive versions (in chronological order):
Notable changes in SharePoint 2010.
Changes in end-user functionality added in the 2010 version of SharePoint include:
Notable changes in SharePoint 2016.
Sources:
Notable changes in SharePoint 2019.
Sources: