To be shallow means to lack depth, either physically or in character and thinking.

A shallow puddle might barely cover your ankles, while a deep lake could be very dangerous if you cannot swim. A shallow dish holds less than a deep bowl. When miners dig a shallow hole, they don't go very far down. The shallows of a beach are those areas near the shore where little kids can play more safely.

But shallow also describes people who care only about surface things rather than what really matters. A shallow person might choose friends based only on looks or popularity, ignoring whether someone is kind or interesting. They might judge a book entirely by its cover or dismiss a movie because the special effects aren't flashy enough. Someone with shallow thinking jumps to quick conclusions instead of considering ideas carefully.

You might describe someone's understanding as shallow if they know just a little bit about many topics but haven't really studied any of them deeply. A shallow conversation stays on the surface, talking only about trivial things like the weather, while a deep conversation explores ideas, feelings, and meaningful topics.

The opposite of shallow is deep in both the physical sense and when describing thinking and character. Being called shallow is not a compliment, suggesting you miss what lies beneath the surface of things.