Aperture

Aperture is a setting in the camera that controls the opening of the lens to determine how much light goes in and controls the depth of field. The bigger the number, the smaller the opening. If the f stop is low then there is more light coming in and it has a shallow depth of field making the background of the subject blurry because it has selective focus. On the other hand, if the f stop is high then there is less light coming in and it has a greater depth of field which makes the background of the subject have more detail and is more clear because it has infinite focus. If the aperture is changed, the exposure triangle shift to one side either being overexposed or underexposed thus making you have to adjust the shutter speed or ISO to zero out the light meter. If the aperture is low then it would need a faster shutter speed but if the aperture is high then the shutter speed would need to be smaller to compensate for the amount of light coming in.