burl means different things to different paople.
A walnut burl is a large tumor like growth on the side of the tree. They were highly prized in colonial days for making bowls. Wild Cherry trees often have such burls, but they rarely get large enough to do much with. Some other species of trees also get "burls" but they are rare.
On walnut trees the grain actually covers the burl in a bowl shape. On the cherry trees, the grain inside looks more like a pine cone that has not yet opened. I have seen a burl that was removed from an apple tree and then air dried for use by a guy whose hobby was turning bowls and candle sticks, etc. Don't know if he ever used it.