Most animals can walk backwards if they want to, even though they don’t choose to do it very often. There are a few birds who can move backwards in small amounts, but only hummingbird can actually fly backwards.
The reason a hummingbird is so good at flying backwards (as well as sideways, up, down, or even just hovering in mid-air) is because of how they use their wings. While most birds flap their wings in an up-down fashion, hummingbirds use a stroke more similar to a circle made with a twisting motion. By using this special wing stroke and being able to fly so many ways, hummingbirds can successfully approach and feed from a flower in any number of directions!