Anything trading, goods or services, with no money exchanged. I love to barter as it is a win win situation for all involved.
Somethings I bartered for -
I made casseroles for her and she serged cloth diapers I had made as she had a serger.
Hair cut for me baby sitting their child.
I also do a lot of trading for fabric with friends. It is not a hard set trading but if I need something they might give it and another time I do the same when they need something or if they see something they like in my home, books, food, etc., I might give it.