When and microphone pickups up sound it does not always pickup the sound from all directions equally, this is by design. An omni-directional microphone will pick up sound from all directions so it doesn't matter in which direction it is pointed. Microphpne that pickup sound in one direction more than in other directions are defined by the relative sensitivity in the different directions. These polar patterns, as they are called, are quite well defined mathematically however often the micropphne does not fully meet these mathematical definitions so are often simply called directional microphones.
Accusound supply a directional microphoine that closely meets the definition of a hyper-carioid polar pattern. Simply put this means the microphone will pickup sound much better at the front compared to the back but also if in a reverberant or non directional sound filed will pickup less ambient sound that a simple carioid polar patternmicrophone. The reason Accusound supply this pattern is because you benifit from the difference between from and back response but you also benefit from better imunity to feedback as less ambient sound is pickedup.
For a fully explanation please see our information pages on microphones.