Professional musicians gather together to jam. You'll find yourself hearing a lot of drums, piano, sax, flute, guitar, harmonica. You can expect much more genres than Jazz only.
Ordering food/drink is not a mandatory, but is a good treat for people who organized it.
It's gonna be crowded after 9pm, so book seats in advance.
Place where you can heal your soul at the end of the week. A lot of talented musicians. People come here to have fun, rest and enjoy. One of the best ways to spend Sunday evening.
P.S. It's a pizza place, so expect certain types of food.