"Windhover" is another name for the common kestrel (Falco tinnunculus). The name refers to the bird's ability to hover in midair while hunting prey. In the poem, the narrator admires the bird as it hovers in the air, suggesting that it controls the wind as a man may control a horse. The bird then suddenly swoops downwards and "rebuffed the big wind". The bird can be viewed as a metaphor for Christ or of divine epiphany. Hopkins called "The Windhover" "the best thing [he] ever wrote". It commonly appears in anthologies and has lent itself to many interpretations. - Summary by Wikipedia