A wheel is a circular object that rotates around a center point called an axle, making it possible to move heavy things with much less effort. Before wheels, people had to drag or carry everything. Imagine trying to move a refrigerator by pushing it across the floor versus rolling it on a dolly: that's the difference wheels make.

The invention of the wheel around 3500 BCE transformed human civilization. Wheels made carts and wagons possible, letting people transport grain, water, and trade goods across long distances. Today, wheels are everywhere: on cars, bicycles, skateboards, suitcases, and even computer mice (the scroll wheel that lets you move up and down a page).

The word also appears in many expressions. When someone talks about the wheels of government or justice, they mean the systems and processes that make things happen, often slowly. Reinventing the wheel means wasting time creating something that already exists. And when people talk about wheels within wheels, they mean complicated systems where many parts affect each other in ways that aren't obvious at first.

As a verb, wheel means to move something on wheels or to turn it around. You might wheel a cart down an aisle, or wheel around to face someone who called your name.

A big wheel is slang for an important or powerful person, while a third wheel is someone who tags along with two friends who'd rather be alone together.