Traditions are longstanding customs and practices. It might be a family tradition to open Christmas presents on Christmas Eve, started because your parents were too impatient to wait.
The noun tradition has Latin roots in the word tradere, which means hand over or hand down. So think of a tradition as something that is handed down from one generation to another. Fireworks on the Fourth of July are a national tradition, and playing your school's fight song at the start of the football game is probably a longstanding tradition designed to get the fans excited for the game.