To curve means to bend smoothly without sharp angles or corners. A river curves through a valley, and a winding road curves around a mountain. When you throw a curveball in baseball, the ball curves through the air instead of traveling in a straight line, making it harder for the batter to predict where it will go.

In math class, you might learn about curves: shapes like circles, parabolas, or spirals that don't have any straight sections. The opposite of a curve is a straight line. Artists use curves to make their drawings look natural and flowing, since very few things in nature are perfectly straight.

The word also appears in the phrase “a learning curve,” which describes how much time and effort it takes to learn something new. A steep learning curve means something is difficult to learn at first. When you first tried riding a bike, you were on the learning curve as you figured out how to balance and pedal.

Teachers sometimes curve test scores, meaning they adjust grades if a test was especially difficult. If the highest score was 85 out of 100, the teacher might curve it so that becomes an A.