A composite number is any whole number greater than 1 that can be divided evenly by numbers other than just 1 and itself. Take 12, for example: you can divide it evenly by 2, 3, 4, and 6, which makes it composite. The number 15 is composite because it divides evenly by 3 and 5. Even 100 is composite since it can be divided by 2, 4, 5, 10, 20, 25, and 50.

The opposite of a composite number is a prime number, which can only be divided evenly by 1 and itself. The number 7 is prime because only 1 and 7 divide into it evenly. But 8 is composite because 2 and 4 also divide into it evenly.

Here's an interesting way to think about it: composite numbers can be broken down into smaller whole-number factors, like taking apart a Lego creation into its individual bricks. The number 24 breaks down into 2 × 12, or 3 × 8, or 4 × 6, or even 2 × 2 × 2 × 3. Prime numbers are like single bricks that can't be broken down further.

The smallest composite number is 4. The number 1 isn't considered composite (or prime), and neither is 0. Mathematicians have studied composite and prime numbers for thousands of years, finding patterns that help with everything from computer encryption to understanding the structure of mathematics itself.