natural action, natural process, activity, action - a process existing in or produced by nature (rather than by the intent of human beings); "the action of natural forces"; "volcanic activity"

negative feedback - feedback in opposite phase with (decreasing) the input

positive feedback, regeneration - feedback in phase with (augmenting) the input

answer, reply, response - a statement (either spoken or written) that is made in reply to a question or request or criticism or accusation; "I waited several days for his answer"; "he wrote replies to several of his critics"