The word duck has several meanings:

1. A water bird with webbed feet, a broad flat bill, and waterproof feathers. Ducks waddle on land but glide gracefully across ponds and lakes. You've probably seen mallards in parks, with the males sporting bright green heads. Ducks can fly long distances during migration, and their waterproof feathers help keep them dry even when they dip underwater for food.
2. To lower your head or body quickly to avoid something. When a baseball comes flying toward you, you duck to get out of the way. You might duck under a low tree branch while hiking, or duck behind a wall during a game of hide and seek. The movement is quick and instinctive, like when you see something coming at you and your body reacts before you even think about it.
3. A strong cotton fabric, similar to canvas. Duck cloth is used to make sturdy items like work pants, tents, and bags that need to withstand rough treatment. You might not hear this meaning as often as the others, but if someone mentions duck canvas or cotton duck, they're talking about this tough, tightly woven material.