A slat is a circuit board used to plug in igniters and is connected to the module using a cable. A slat does not contain integrated circuits or logic and will always fire at the same time as the module to which it's connected. A slat does not add any additional unique cues but acts as a mirrored position to the module by firing at the same time. A single module can have multiple series or parallel slats connected to it.
See Continuity Clarified for more information on series and parallel wiring and our Slats Video, below, to learn more about slats.