How Come www Has Number as in http://www31.website.com?

How come I saw some web site has some number after www, how can they do
that?

i.e. http://www31.website.com, http://www52.website.com

If this is the case, then it can be anything? Like
http://aaa.website.com ? I know the protocol needs to be http.

Usually, it should be just http://www.website.com

Please advise. thanks!!

[TELECOM Digest Editor's Note: You are correct that it usually is just
'www' which means 'world wide web' and years ago, when the web was a
new thing, most all files used by it were put in a directory called
'www'. But that is not necessary. You can reach me for example either
with or without 'www' on the front. If he is saying 'www some number'
then a dot and something else thats just because he chose to use that
name, maybe to confuse the issue a little. The computer directories
do not care what they are called as long as there are no 'illegal'
characters in the name such as / or \ or " or . or , etc. PAT]

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