a meeting of a group of musicians, especially jazz musicians, to play for their own enjoyment.
an impromptu jazz performance or special performance by jazz musicians who do not regularly play together.
Origin of jam session
Also called jam.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
slang an unrehearsed or improvised jazz or rock performance
Word Origin for jam session
C20: probably from jam 1
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012