Woof is the deep, gruff barking sound a dog makes. When your neighbor's big dog sees a squirrel in the yard, it might let out a loud woof or a series of woofs.

Different dogs make different sounds: small dogs might yap or yip, while medium and large dogs tend to woof or bark. A woof is usually lower and more throaty than a yap. Think of how a Golden Retriever sounds compared to a Chihuahua.

People use “woof” as a verb too. You might say a dog woofed at the mail carrier, or that it woofs whenever the doorbell rings. Sometimes people jokingly use the word themselves, like saying “woof woof!” when greeting a friend's dog.

The word can also refer to threads in weaving. When you weave fabric on a loom, the woof threads (also called the weft) run horizontally, crossing over and under the vertical threads called the warp. But unless you're studying textiles or helping someone weave, you'll almost always hear woof used to describe the sound a dog makes.