A zone array sound system is a particular type of PA installed at venues that have issues with noise levels. The speakers are installed in the ceiling above the dance floor and the sound is then directed onto the dance floor, rather than out towards your guests. The quality of this type of system is often poor with no low-end sound, especially when compared to the band's own PA system. Many bands refuse to perform with zone array sound systems, so it's worth checking with them if your venue has one installed.