1630s, "condition of being concealed," from latent + -cy. Meaning "delay between stimulus and response" is from 1882; computer sense (latency time) is from 1954.
latency la·ten·cy (lāt'n-sē)n.
The state of being latent.
In conditioning, the period of apparent inactivity between the time the stimulus is presented and the moment a response occurs.
See latency phase.