In Japanese, a word roughly meaning "bonus" or "extra". Like the word anime itself, the Western anime audience has adopted the word omake to refer to such bonuses or extras that go along with things of a specific Japanese nature: Anime, manga, video games, fan sites, etc.
Examples of omake are: Bonus material at the end of an anime tape or in a section of a DVD menu, such as making-of movies, image galleries or previews. A section of a web site with all the other side stuff that doesn't fit into one of the main categories. Bonus items packaged with a video game, such as maps or soundtrack CD's.
Roughtly pronounced: oh-mah-kay. (see Japanese Word Pronunciation)