The Aperture is the “value” given to a certain condition in your camera, directly relating to the amount of light passing through to the film or sensor for X amount of time.
In every lens there is an iris that controls the amount of light that reaches and exposes the FILM, CCD or CMOS. The F-STOP relates to the size of the “hole” or the amount of light the iris lets through. The aperture also has a direct influence on DEPTH OF FIELD (DOF) and/or SHUTTER SPEED. The minimum aperture also has an influence on AUTO FOCUS performance and ability.