Depth is the distance from the top or surface of something down to the bottom. A swimming pool's depth tells you how far down the water goes: the shallow end might have a depth of three feet, while the deep end could be twelve feet deep. Ocean depth is measured from the water's surface down to the seafloor, which in some places reaches depths of over six miles.

The word also describes how thorough or profound something is. When a book has depth, it explores ideas carefully and seriously, going beyond surface observations to examine underlying meanings. A conversation has depth when people discuss meaningful topics and share genuine thoughts. Teachers appreciate answers that show depth of understanding, where you explain not just what happened but why it matters and how it connects to other ideas.

You might hear someone described as having depth of character, meaning they're thoughtful and interesting rather than shallow or superficial. A shallow person only cares about appearances, while someone with depth thinks about what really matters. Scientists study problems in depth when they investigate thoroughly. Musicians add depth to their performances by playing with feeling and nuance, bringing emotional expression to the music beyond technical accuracy.

The phrase out of your depth means being in a situation that's too difficult or complex for you, like a beginning swimmer accidentally drifting into water that's too deep.