I will try dude. A Sing a Round is when people come together in a pub or a function room and go round the room in some kind of order, playing tunes or singing songs, the choice is up to the person whose turn it is, and people can join in. Like at The Bull in Barton Beds. A session is where everyone plays together English, Irish, or Scots etc folk tunes, not many if any songs. An open mic night is like a folk club where people sit in a room and go up to the front of the room, infront of people and play. If you are near Dunstable on Fri Sept 03 at 8.30pm and or Sat Sept 04 12.00-06.00 pm come to The White Horse Finbars in the High st North for more examples.