Combat takes place in a series of turns and rounds. A turn is considered a five-second space of time (for ease of calculation, it's probably actually closer to two or three seconds in real time), and a round, although it may be more or less than six turns, is considered to be half a minute. Whenever you see “ten seconds” or “one minute” given in the rules for activity taking place out of combat, these same actions will take two turns and two rounds, respectively, in combat. A turn is the time one person takes to act, and a round is the time it takes for one person’s turn to come back around. Two people engaged in combat against each other where one is attacking and the other is defending spend only one turn doing so.
Combat turns do not always, like in many other games, take place one character at a time. Every time someone takes a turn, other characters can move, fire, begin casting a spell or charging a psionic ability, or any number of other activities. This requires that everyone keep track of what they are doing, and works best if tabletop miniatures are used.
A “turn,” in addition to being five seconds long, is considered the approximate time required for one person to act in combat. During this turn, combatants may have moved around the battleground, bullets may have been expended, spell or psionic energy may have been gained, gunmen may have fired, or a blazing fire may have spread or waned.