what is this

[Aymen++]

when we go to specified forum in this website, we see in the address bar there is two variables, the s & forumid, what is the s variable and for what is it used?

[raf]

Not sure why you post this here.
The thing in teh adressbar is called the querystring. The variables stand for
s = SID (session id) (if you have cookies enabled, the s will almost always be empty, once you're off the first page)
threadID = the threadid (probably the primary key value from the threadstable)

[Aymen++]

but i tried to make authontication page like this one of this forum, when the user login and press the link to the forum the SID appears automaticaly in the address bar!, why? i only passed the forumid to the next page...
you can see that on:
http://members.lycos.co.uk/aymenplusplus/index.php