Gray level
From The Glossary of Digital Photography
A number representing the brightness or lightness of a pixel. The number runs from black, where gray level equals 0, to white, where gray level equals 255, for a total of 28,or 256 levels.

ONLINE GLOSSARY OF DIGITAL PHOTOGRAPY
A number representing the brightness or lightness of a pixel. The number runs from black, where gray level equals 0, to white, where gray level equals 255, for a total of 28,or 256 levels.