Swum is the past participle of the verb “to swim.” You use it when describing swimming that happened in the past, especially with helping verbs like “have,” “has,” or “had.”

If you went to the pool yesterday, you might say “I swam twenty laps.” But if you're talking about your total experience up until now, you'd say “I have swum in three different oceans.” The difference is subtle but important: swam stands alone as the simple past tense, while swum needs a helper verb and often connects past action to the present moment.

You might hear someone say “She has swum competitively for five years” or “By the time we arrived at the beach, they had already swum out to the raft.” The word signals that the swimming is complete.

Many people mix up swam and swum, using them interchangeably, but careful writers and speakers keep them distinct. Think of it this way: you swam (simple past), but you have swum (past participle). It's the same pattern as “I ran” versus “I have run,” or “I began” versus “I have begun.” Once you notice the pattern, it becomes easier to use swum correctly in your own writing and speech.