Nikon N6006 - Manual (Page 162)

SLR
Single-Lens Reflex. A type of camera in which you look
through the camera’s lens as you view through the camera
finder. Other camera functions, such as light metering and
flash control, also operate through the camera’s lens.
Spot metering
Sensitivity is concentrated on the approx. 3.5mm-diameter
circle in the center of the camera’s viewing area. Effective
when precise measurement of a special portion of the subject
is required.
TTL
Through-The-Lens. Most SLR cameras have built-in meters
which measure light after it has passed through the lens, a
feature that enables exposure readings to be taken from the
actual image about to be recorded on film, whatever the lens’
angle of view and regardless of whether a filter is used.
TTL auto flash
The camera’s light sensor measures flash light as reflected by
the subject on the film and shuts off the flash when measure­
ment indicates correct exposure. Because the sensor that con­
trols the flash receives light through the lens, TTL auto flash
can be used for bounce photography, fill-in flash, multiple flash
photography, etc. An additional advantage of TTL auto flash is
that you can use a wide range of aperture settings, while
ensuring correct exposure.