A divisor is a number that divides evenly into another number, leaving no remainder. When you divide 12 by 3, you get exactly 4 with nothing left over, which makes 3 a divisor of 12. The other divisors of 12 are 1, 2, 4, 6, and 12 itself.

Finding divisors helps you understand how numbers break apart. Some numbers, like 12, have many divisors because they can be divided in lots of ways. Others, like 7, have only two divisors: 1 and 7. Numbers with exactly two divisors are called prime numbers, and they're building blocks of all other numbers.

Divisors matter when you're sharing things fairly. If you have 24 cookies and need to divide them equally among friends, you can only do it without breaking cookies if the number of friends is a divisor of 24. With 6 friends, everyone gets 4 cookies. With 5 friends, you'd have cookies left over because 5 isn't a divisor of 24.

In a division problem like 20 ÷ 4 = 5, the number 4 is the divisor, 20 is the dividend, and 5 is the quotient.