This means when a whole bunch of musicians get together play some chords for about a minute saying random lyrics and then go on playing for 19 more minutes.
When a group of bros take turns having sex with a jar or squeeze bottle of jam or jelly (preferably squeeze bottle). Can substitute marmalade as well. No preserves for fear of chunks in urethra.
I got together with my old college roomates this weekend and we had a solid 2 hourjam session.