Customs are taxes, or duties, that you sometimes have to pay when you import goods from another country.
When you return home from a trip to another country, you have to clear customs by talking to a customs officer and declaring everything you bought or got as a gift while you were traveling. If you're bringing in a lot of stuff, you may have to pay customs — the duty on imports. Customs are a source of income for a country, and they also provide control over what’s coming in.