Trim - Nikon D300 Complete Manual

Review:
Zoomed:
The modified version of your image will appear with a special
icon (paintbrush):

Trim

Sometimes you'll take a picture that covers more area than
you want in the final image (for example, you couldn't get
closer to your subject or didn't have a long enough telephoto
lens). Eventually, you'll want to crop that image to get rid of
the extraneous parts. The D300 allows you to do that in
camera (though with some size constraints that might not
match what you want to do).
Thom Hogan's Complete Guide to the Nikon D300
V1.02
Page 715