Why do some domains use www2 and www3 in the prefix? [duplicate]

www2, www3 e www4 hostnames are mirrors of the original server, the main purpose of this technique is to reduce server load, load balancing, or maintain the service online when the original server needs to be updated.

As the member @GuilhermeNascimento quoted the hostname numbers are sequential.

What is a hostname : It is the name given to the computer, it is used to identify a machine on the network, more easily than an IP number, in the same way as two bodies can not coexist in the same space, two machines can not have equal names on the same network.

What is a subdomain : These are the branches of the main domain, something that is widely used on large sites. In the site [support.yourdomain.com], for example, [* .yourdomain.com] is the domain, and "support" is the subdomain, which has the function of leading the user directly to the specific section of the site .

Sources:

• Subdomain
• Hostname