A louse — the name for lice if you're talking about just one of them — is a tiny gray and brown bug that's as big as a sesame seed.
If you get a case of them, they itch like mad. While they're living on your scalp, they eat your blood and lay eggs for more lice.
© 1995-2015 KidsHealth® All rights reserved. Images provided by iStock, Getty Images, Corbis, Veer, Science Photo Library, Science Source Images, Shutterstock, and Clipart.com