Nikon Autofocus Speedlight SB-24 - Manual (Page 135)

Exposure control for available light
Programmed: the automatic exposure system controlling both
the camera's shutter and the lens' aperture.
Shutter priority: user selects shutter speed and automatic
system chooses aperture for correct exposure.
Aperture priority: user selects aperture and automatic system
chooses shutter speed for correct exposure.
Manual: user follows the meter's recommendations for shutter
and aperture settings.
Fill-flash
A method of flash photography which combines flash illumina­
tion and ambient light, but does not necessarily attempt to
balance the two types of illumination.
Flash synchronization
The timing of the flash so it fires coincident with the operation of
the camera’s shutter. There are two types of synchronization:
NORMAL, which fires the flash at the start of the exposure, and
REAR synchronization, which fires the flash at the end of the
exposure.
Guide number
A calculated number which indicates the relative power of a
flash unit.