HTTP stands for HyperText Transport Protocol. HTTP servers are commonly used for serving hypertext documents, as HTTP is an extremely low-overhead protocol that capitalizes on the fact that navigation information can be embedded in such documents directly and thus the protocol itself doesn't have to support full navigation features like the FTP and Gopher protocols do.
A file called "foobar.html"
on HTTP server "www.yoyodyne.com"
in directory "/pub/files"
corresponds to this URL:
http://www.yoyodyne.com/pub/files/foobar.html
The default HTTP network port is 80; if a HTTP server resides on a different network port (say, port 1234 on www.yoyodyne.com), then the URL becomes:
http://www.yoyodyne.com:1234/pub/files/foobar.html