Multiple sessions & Authlogic

From http://github.com/binarylogic/authlogic_example#readme - - - - So lets assume you are setting up a session for your User model. You can call this anything you want, but I recommend naming it after the model you are authenticating with, this way if you want to add multiple session models down the road you can easily do this without have name clashes. - - - -

What does "multiple sessions" and or "mutiple sessions model" mean in this context?