a bird, most often a small wild one, and birds taken together as a class
This is the ordinary Hebrew word for a bird. It leans toward the smaller, common birds a person would actually see fluttering, nesting, or caught in a trap, rather than the great birds of prey, which have their own names. The word probably began as an imitation of the sound a small bird makes, the chirp or twitter, and it keeps that everyday, close-to-the-ground feel throughout the Bible.
It is used two ways that shade into each other. Sometimes it names birds as a whole category, the flying creatures listed alongside beasts, fish, and creeping things, or the flocks that nest in trees and fill the sky. Other times it zeroes in on a single small bird, the sparrow on the rooftop, the bird darting from a snare, the mother sitting on her nest. Because the same word covers both, the difference is one of focus, not of two unrelated meanings.
The small bird became one of Scripture's favorite pictures of a fragile, hunted, or lonely life: safe only if it escapes the trapper, exposed on a housetop, longing for a nest. That vivid smallness is why poets and teachers reach for this word so often.