Cardioid microphones reject sound from behind them and are more sensitive to sounds produced in the direction they are facing. The rough shape of their optimal range is similar to a cartoon heart shape with its point facing away from the microphone. This is useful for performers on stage because the microphone does not pick up sound from the stage speakers, which can produce feedback.
Hypercardioid microphones are development of cardioid microphone concept further isolating sounds from the front and eliminating more sound from the sides. Hypercardioid pattern allows a limited amount of sound from behind the microphone to be detected as opposed to cardioid which aims to cut rear sound out completely.
The supercardioid pattern brings the cardioid principle to its extreme, allowing only sound from the front to be detected and aiming to completely shut out sound produced from the side. This design allows stage monitor speakers to be set louder before feedback occurs through the microphone.
Cardioid microphones are favored for use by live bands, radio stations and journalists, because they isolate the intended sound while removing background noise. In a radio station studio, the producer can ideally isolate the different voices and set up levels or volume for each individual - this would not be possible if the studio microphones were to pick up all of the voices in the room at the same time. Journalists use cardioid microphones when interviewing people to reduce the amount of background noise picked up on the tape.
Omnidirectional microphones pick up sound 360 degrees of sound. They are mostly used for picking up ambient sound or background noise - for example at sporting events when TV producers want a microphone to pick up the sound of the crowd. Omnidirectional microphones are used in recording studios for picking up group voices but typically not used for live recording because of their tendency to easily cause feedback.