Ground has several important meanings:

1. The surface of the earth beneath our feet. When you walk outside, jump rope, or play soccer, you're moving on the ground. Pilots talk about being “on the ground” when they've landed safely. The ground can be dirt, grass, concrete, or any other surface that makes up the earth's floor.
2. To punish someone by restricting their freedom, usually keeping them at home. When parents ground their child, they might say “You're grounded for a week,” meaning no going out with friends, no video games, or other privileges are taken away.
3. The reason or basis for something. When a lawyer argues a case, she needs grounds for her argument: solid reasons that support her position. A teacher might give you grounds for improvement by explaining exactly what needs work. If someone makes an accusation “on the grounds that” you broke a rule, they're stating their reasoning.
4. In electricity, a safety connection that helps prevent shocks. Electrical outlets have a ground wire that redirects dangerous electricity safely into the earth if something goes wrong.

The word can also mean to teach fundamentals, as in “grounding someone in mathematics,” or to keep aircraft from flying during bad weather.