Sung is the past participle of the verb sing. It's the form you use with helping verbs like “have,” “has,” or “been.” You'd say “I have sung that song many times” or “The national anthem has been sung before every game this season.”

The distinction between sang and sung trips up many people. Here's the pattern: use sang for simple past (“She sang beautifully yesterday”) and sung when there's a helping verb (“She has sung in three concerts this year”).

You might hear sung in phrases like “a hero sung in legend,” meaning someone celebrated in old stories and songs, or when talking about music that's been performed: “That hymn has been sung in churches for centuries.” The word connects to one of humanity's oldest art forms, since people have been singing, and therefore have sung, for as long as we've had language.