what exactly is resident set size in /etc/security/limit.conf and ulimit -m?

[Zhang Weiwu <zhangweiwu@realss.com>]

Having read the manual and examples on the Internet, still confused.

Some suggest it is the limit of a session (as
http://www.svantech.com/node/4.

    * Was it the size limit of a single process?
    * Was it the size limit of a single session?
    * If it is for a session, what counts a session? Is a single login
      to gnome-session a session? Is every terminal window I open in
      xterm a session? Is it a login session or a shell session? or a
      screen session? So if I set rss to 1GB, does it mean I can use 2GB
      if I run two 1GB-sized program each in a separate xterm window?

I believe those who knows how kernel works has the right assumption of
what 'session' is, but that is not obvious to users who use command line
mostly on user-space. Please hint! Thanks.