WWW2

WWW2 and WWW3 are hostnames or subdomains, typically used to identify a series of closely related websites within a domain, such as www.example.com, www2.example.com, and www3.example.com; the series may be continued with additional numbers: WWW4, WWW5, WWW6, and more. Traditionally, such websites are mirrors used for server load balancing.
Purpose.
The purpose of WWW2 domains or domain prefixes with numbers are so it can run using the same domain but balance the load to different servers, often used as 'mirrors'. Furthermore, WWW2 or similar domain prefixes can also be used if the main server is under development. This way the server's visitors won't notice any downtime.