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1.
noun: The partial surface of a brick, painted in a mosaic style in order to represent a pixel used in pixel art.

Brixel is a portmanteau of brick and pixel.

A wall of brixels is called brixel art.
"Yo, did you see that brixel art someone did on the side of the library?"
"Yeah man, that is some hardcore brixeling."
by Flamescape September 18, 2007