Tense refers to the time when the action of the verb occurs. The action can occur in one of three time periods: past, present, or future. They form a time line.
Ex: I ate, I eat, I will eat.Aspect refers to the time when the action of the verb occurs either across or between those periods. That is, the times on the time line can be extended (progressive aspect) or combined (perfect aspect):
The action is continuous.
There are more examples here: Verb - Simple English Wikipedia, the free encyclopedia
Ex: When Sam called, I was eating.Perfect aspect
The action happened at some unknown time between then, the past, and now, the present time of speaking.
Ex: I have eaten today.
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