APA Dictionary of Psychology

an encounter group that meets in seclusion for a single extended session, usually varying from 6 hours to several days, on the theory that this will elicit more intense interactions, foster a greater sense of intimacy and sharing, and encourage a freer expression of feelings as the time elapses than would a series of shorter, interrupted sessions. Such groups are often organized around addressing a single issue or related set of issues. See also time-extended therapy.