A tradition was a custom that was passed down from one generation to the next within a group or society.
In 2259, Duke was promoted from ensign to lieutenant. Spock mistakenly referred to Duke as an ensign after the promotion, which according to Nurse Christine Chapel meant that Spock had to buy him a drink in accordance to Starfleet tradition. (SNW: "All Those Who Wander")
According to Amerind tradition, a tribal priestess and medicine chief were always joined in marriage. (TOS: "The Paradise Syndrome")