A hill is a natural rise in the land, higher than the ground around it but not as tall as a mountain. When you climb a hill, you walk upward until you reach the top, then downward on the other side. Hills can be grassy, rocky, forested, or bare, and they form from various geological processes over millions of years.

The difference between a hill and a mountain isn't perfectly defined, but mountains are generally much taller, steeper, and more dramatic. A hill might take you ten minutes to climb, while a mountain could take hours or days. San Francisco is famous for its steep hills that make your legs burn when you walk up them. The English countryside is known for its gentle, rolling hills covered in green grass.

Hills matter in human history: armies fought to control hilltops because they offered views of approaching enemies. Cities were built on hills for defense and to avoid flooding. Even today, a house on a hill often costs more because of the view it provides.

You'll also hear hill used figuratively. When something is difficult, people say it's an uphill battle or an uphill climb. Going downhill can mean getting worse, though going down an actual hill is usually the easier part. And when someone says they're over the hill, they mean they're past their prime, though plenty of people would disagree with that assessment.