Reaction time or response time was the amount of time it took for an individual's reflexes to react to stimuli.
Malcolm Reed preferred to exercise in the evenings, as he found his reaction time to be quicker. (ENT: "Harbinger")
In 2266, following one simulated attack, Dave Bailey informed all decks of USS Enterprise that they should ready themselves to improve their reaction time on the second attack. (TOS: "The Corbomite Maneuver")
According to Doctor McCoy's log in 2267, prior to his stay on the Shore Leave Planet, Captain Kirk's reaction time was down nine to twelve percent. (TOS: "Shore Leave")
In 2268, Deela was able to easily evade Kirk's phaser fire, as her reactions were too fast for his weapon, which she dismissed as "crude". (TOS: "Wink of an Eye")
While training for entrance into Starfleet Academy's Academy preparatory program in 2371, Nog managed to improve his reaction time by nearly twenty percent. According to him, he had five percent more before he reached the cutoff. (DS9: "Facets")