A lean-to is a simple shelter with a sloped roof that leans against something else for support, like a tree, a rock face, or the side of a building. Picture a piece of plywood or canvas propped at an angle against a wall: one end rests on the ground while the other end is held up by whatever it's leaning on.

In camping, you might build a lean-to using branches and leaves to create an emergency shelter from rain or wind. The roof slopes down from the support, letting water run off instead of pooling on top. Some cabins have lean-to additions built onto their main structure, creating extra storage space or a covered porch area without the expense of constructing a full room with four walls.

The name makes perfect sense once you see one: the shelter literally leans to one side for support. While a lean-to won't protect you as well as a proper building, it's quick to construct and uses minimal materials, which is why campers, hikers, and builders have relied on this design for centuries.