Josh Stotts

John Heino

 jam session

noun 1. a meeting of a group of musicians to play for their own enjoyment. 2. an impromptu performance or special performance by  musicians who do not regularly play together.  You could add to that citation from the Random House Dictionary:  a meeting of musicians and aspiring musicians of all ages, skill levels and walks of life, several times a week at an iconic Duluth eatery.