The noun activity has 6 senses (first 6 from tagged texts)
1. (614) activity -- (any specific behavior; "they avoided all recreational activity")
2. (137) action, activity, activeness -- (the state of being active; "his sphere of activity"; "he is out of action")
3. (52) bodily process, body process, bodily function, activity -- (an organic process that takes place in the body; "respiratory activity")
4. (22) activity -- ((chemistry) the capacity of a substance to take part in a chemical reaction; "catalytic activity")
5. (19) natural process, natural action, action, activity -- (a process existing in or produced by nature (rather than by the intent of human beings); "the action of natural forces"; "volcanic activity")
6. (1) activeness, activity -- (the trait of being active; moving or acting rapidly and energetically; "the level of activity declines with age")