A mind swap or body swap was the occurrence of one person's consciousness or neural pattern, being transplanted to another's body and vice versa.
In 2259, Lieutenant Commander Spock's katra was inadvertently swapped with his fiancée, T'Pring's for a brief time when they attempted to conduct the Vulcan soul-sharing ritual. (SNW: "Spock Amok")
In 2269, Captain James T. Kirk's consciousness was swapped with Dr. Janice Lester's through the use of a machine Dr. Lester found on Camus II. The procedure was described as a life-entity transfer and only lasted a short time. (TOS: "Turnabout Intruder")
In 2384, Vice Admiral Kathryn Janeway's neural pattern was swapped with Dal R'El's when the latter attempted to facilitate a telepathic link via Dal's Organian genes. (PRO: "Mindwalk")
A similar process known as selected DNA exchange works by altering the subjects' bodies to resemble each other rather than transferring minds. (VOY: "Vis à Vis")
In the novel Star Trek Log 10, a transporter malfunction caused a landing party consisting of Kirk, Spock, Sulu and Uhura to switch bodies. Kirk was in Sulu's body, Sulu was in Spock's body, Spock was in Uhura's body and Uhura was in Kirk's body. Scott eventually found a way to reverse the process.