It's where it picks up sound from. omni directional and unidirectional, omni- all around you, uni- in the direction it's facing, in kind of a heart shape. hyper cardioid mics or shotgun mics are highly unidirectional, they have real long thin heart shaped pick up patterns so you can really isolate sounds. I would never, ever, ever use an onboard microphone unless i was trying to make fun of badly made movies like a blair witch spoof, which i would never do, so i'm left with never ever...