Jam Sesh 

When at least semi-experienced musicians get together and pull songs out of their ass, working all together non-verbally. Almost always involves hilarious bullshit lyrics.

Good jam sesh last night man, way to pull that riff out of your ass

Jam Sesh by bassjesus June 17, 2014

Jam Sesh 

A slang term used by douchebags to describe a jam session. Typically used by shitty/non musicians.

Hey man, wanna get together tonight and have a wicked jam sesh?

Jam Sesh by JayDoopy April 1, 2019

Jam Sesh 

Subconsciously dancing to a song then noticing that others are doing the same, which only makes the group jam more enthusiastically.

The Black Eyed Peas can usually entise a jam sesh.

Jam Sesh by ahhhsuraah January 20, 2011