A duck is a bird that spends much of its life on or near water. You can sometimes see whole families of ducks paddling across lakes and ponds.
Ducks can be wild or domesticated — if you keep ducks in your yard, you'll need to provide them with at least a small body of water. When the word duck is a verb, it means "to bow or dip suddenly," like when your kite plunges suddenly and you duck to avoid getting hit in the head. You can duck figuratively, too: "Don't you dare duck out of helping me clean up after the party!"