(1) The time it takes for a pixel to change color. See
pixel response time.
(2) In an interactive session, response time is the time it takes for a local computer or remote server to respond with an answer or confirmation after the user presses Enter. In a session that requires multiple entries such as filling out an order form or answering a questionnaire, extremely fast response times are necessary. In a search on the Web, the response time can be a bit slower, but any results that take more than a couple seconds is considered mediocre. See
Doherty threshold and
real-time system.