Stone is hard, solid rock, especially pieces small enough to pick up. When you find a smooth stone by a stream or skip a flat stone across a pond, you're holding rock that nature has shaped and weathered over time.

People have used stone as a building material for thousands of years because it lasts so long. The pyramids of Egypt, built from massive limestone blocks, still stand after 4,500 years. Medieval castles, stone bridges, and ancient temples survive while wooden structures from the same eras have long since rotted away. Stone buildings can last for centuries with little maintenance.

Stone also refers to the hard seed or pit inside certain fruits. A peach stone, cherry stone, or avocado stone is the hard center you can't eat.

The word appears in many expressions. If you have a heart of stone, you show no sympathy or emotion. When something is set in stone, it cannot be changed. To leave no stone unturned means to search everywhere and try everything to find what you're looking for. And if you're stone cold, you're completely cold, not even a little bit warm.

Different types of stone include granite, marble, limestone, and sandstone. Each has different properties that make it useful for different purposes, from countertops to sculptures to gravel roads.