warm-up n.

"act or practice of exercising or practicing before an activity," 1915; earlier in literal sense, "a heating" (of something), 1878, from verbal phrase warm up, which is from 1868 in the sense "exercise before an activity." Earlier in reference to heating food (1848), and earliest (c. 1400), figuratively, of persons. In reference to appliances, motors, etc., attested from 1947.