thumb|right|296pxMicrophones are designed with a certain polar patterns. A polar pattern is the area around the microphone that will pick up the best audio signal. Each polar pattern is designed for a specialist purpose, whether that is to pick up the overall ambience of an environment (Omni), or to pick up precise sound source (cardiod) while reducing unwanted audio. Here are some interesting clips, websites and PDF's which will teach you some more.
Here is a detailed PDF,