Snaga, translated as "slave" in the Appendices, is not a personal name but a term used by Uruks to describe lesser Orcs. Used among others by Uglúk to a scout of the Uruk-hai and by Shagrat to one of the Orcs of the tower of Cirith Ungol.
In Peter Jackson's film trilogy the name Snaga is associated with (though never mentioned by name in the movie) a particular Orc in The Two Towers, who is part of Grishnákh's company, and wants to eat Merry and Pippin to whet his hunger. He is decapitated by Uglúk and cannibalized by the Uruk-hai. His voice is provided by Andy Serkis.
Read more about this topic: List Of Middle-earth Orcs