A timeout is a break in gameplay other than between sections (such as halves, or regulation and overtime). Depending on the rules in use, they can typically be called by players (sometimes only captains) or coaches. Teams are usually limited in their number of timeouts and the duration(s) thereof. Officials may also pause gameplay, which is generally not limited in any way but is rare.
Again depending on rules, team-called timeouts might be used to substitute players in and/or out, for coaches (or others) to advise teams, to discuss possible protests, in hopes of stopping an opponent's momentum, or for other reasons. Officials' timeouts are usually used to review rulings, look at long answer lines carefully (especially in timed play), or verify rules.