Swam is the past tense of the verb swim. It describes the act of moving through water using your arms, legs, and body, but in the past. If you went to the pool yesterday and propelled yourself through the water, you swam. If your friend crossed the lake last summer, she swam across it.

You might say “I swam ten laps this morning” or “The dolphin swam alongside our boat.” The word tells us that the swimming already happened and is finished. It's different from swim (happening now, like “I swim every day”) and swum (used with helping verbs like “have,” as in “I have swum in that lake before”).

People sometimes mix up swam and swum, but here's an easy way to remember: if you can put “have” or “has” before it, use swum (“I have swum”). If you can't, use swam (“I swam”).