Banana flowers (a.k.a. banana blossoms) are, as the name suggests, the blossoms from a banana tree. Like bananas, they are wonderfully edible. The darker, tough husks on the outside simply need to be stripped away to reveal the tender, yellow-green leaves inside. The youngest specimens can be simply chopped and used in salads (like this Banana Blossom Salad). Banana flowers can also be used in soups (like this Banana Flower Soup) or stir-frys.
Note that banana flower leaves will turn brown or black if left to sit exposed to air for any length of time. So after you remove the tough outer layer and separate or chop the inner leaves, put them in a bowl of acidulated water (add several tablespoons of lemon juice or vinegar or a bowl of water) to minimize the browning.