The mouth is the opening in your face where food goes in and words come out. It's bordered by your lips and contains your teeth, tongue, and the beginning of your throat. When you eat, your mouth breaks down food with your teeth and mixes it with saliva to start digestion. When you speak, your mouth shapes the sounds your vocal cords make into recognizable words.

The word mouth also describes openings in other things. A river's mouth is where it flows into the ocean or a larger body of water, like the mouth of the Mississippi River where it empties into the Gulf of Mexico. A cave has a mouth at its entrance. A bottle or jar has a mouth where you pour liquid in or out.

People also use mouth as a verb meaning to say something without really meaning it, or to say it silently. If someone is just mouthing the words to a song, their lips are moving but no sound is coming out. When a student mouths off to a teacher, they're speaking disrespectfully or talking back in a way that can get them in trouble.

The phrase “watch your mouth” is a warning to speak more carefully or politely. And if someone is all mouth, it means they talk big but don't follow through with action.