Shampoo is a soapy liquid you use to wash your hair. When you squeeze shampoo into your hands and rub it through your hair, it creates foam that lifts away dirt, oil, and anything else that's made your hair greasy or grimy. After massaging the shampoo into your scalp and hair, you rinse it out with water, leaving your hair clean and fresh.

For most of history, people washed their hair with plain soap or didn't wash it very often at all. Modern liquid shampoo as we know it was invented in the 1930s.

Today's shampoos often contain special ingredients for different hair types: some add moisture for dry hair, others help with dandruff, and some claim to make hair shinier or stronger. The word can also be a verb: you shampoo your hair, or shampoo the carpet when you clean it with special foam.