Equivalent exposure is a digital photography term used to describe the effects generated when the aperture and shutter speed are changed while keeping the lighting the same for proper exposure. A higher shutter speed uses a lower aperture and vice versa.
Many modern cameras incorporate intelligent exposure technology that does many of the aperture to shutter speed calculations automatically. Before taking a picture, set the shutter speed or aperture priority. By doing this, the camera automatically adjusts the other setting for equivalent exposure due to the intelligent lighting sensors within the camera. This is very useful when lighting conditions are variable.