A nest is a shelter or other structure that an animal uses for laying eggs or giving birth. If a bird is collecting string and straw and twigs in your yard, she's probably building a nest in a nearby tree.
Large birds of prey build nests that can be six feet high, in trees or on buildings, and up to three feet wide. Owls often make nests in tree hollows, while orioles build elaborate hammock-like nests that hang from branches. Foxes, mice, and raccoons also build nests, and people can make nests too, cozy spots to settle for a nap. As a verb, nest means "to build a nest or fit inside something larger."