Fifteen is the number that comes after fourteen and before sixteen. It's written as 15 in digits and represents three groups of five.

Fifteen shows up everywhere in daily life. In many places, students are in high school around age fifteen. If you're saving money and have three five-dollar bills, you have fifteen dollars. When you're fifteen minutes late, you've missed a quarter of an hour.

The number appears in many games and sports: in some scoring systems in tennis, the first point in a game is called 15 on the scoreboard. In pool, fifteen balls (numbered 1 through 15) are spread across the table at the start.

Mathematically, fifteen is interesting because it's the sum of the first five counting numbers: 1 + 2 + 3 + 4 + 5 = 15. It's also divisible by 1, 3, 5, and 15, making it what mathematicians call a composite number.

When you turn fifteen, you're exactly halfway between being ten and twenty. You're in your teenage years, with several years before becoming an adult.