Steepness describes how sharply something slopes or rises. A gentle hill has little steepness: you can walk up it without much effort. A mountain trail with high steepness forces you to lean forward and work hard with every step. Ski slopes use steepness ratings to warn skiers which runs are challenging: a steep slope might be marked with a black diamond, while a gentle one gets a green circle.

In mathematics, steepness describes how quickly a line rises or falls on a graph. A line with high steepness shoots up rapidly, while one with low steepness rises gradually. Engineers and architects think carefully about steepness when designing roads, ramps, and staircases: too much steepness can make them dangerous or impossible to use, especially for people in wheelchairs.

The word can also describe how quickly something increases. If the steepness of prices rises sharply, things become expensive very fast. When someone faces a steep learning curve, they need to learn a lot in a short time, like the challenge of climbing a steep hill rather than strolling across flat ground.