Windows
1) Holes put in walls of buildings, often rectangular or square, which contain glass. They are there to both let in light and provide a nice view of the outside world.

2) The most popular Computer Operating System today, 'invented' by Microsoft Corporation. It has good ease of use and a wide range of commercial software available. 

Many computer experts ('nerds') say that Windows is bloated, unstable, insecure and requires users to upgrade too often. However, Windows is a perfectly fine Desktop OS for non, semi computer literate people and gamers, provided they can install a firewall, virus scanner and spyware remover.

However, for people more experienced with computers or for business applications, other Operating Systems such as Linux or *BSD are faster, more stable and secure, cheaper (erm, free) and more customisable than Windows. 

Unfortunately, most of these OSes are harder to use and cannot run Windows software, although there are good free alternatives to Windows software for OSes like Linux such as Open Office for MS Office and Mozilla for IE.
"I bought a new top-of-the-line gaming PC and it came with Windows XP, natch"