Sly is an adjective, meaning one of the following:
Clever in practical matters.
Hiding ones true intentions or goals.
Its synonyms are "cunning" and "roguish".Sly is also a proper masculine name, short for Sylvester. It is the name of several famous persons:
Sly Stone, American musician, frontman for Sly & the Family Stone
Sylvester "Sly" Stallone, American actor.
Sylvain Grenier, Canadian professional wrestler.
William Sly, Elizabethan actor and colleague of William Shakespeare.
Sly is the title of an opera by Ermanno Wolf-Ferrari.Sly is also the first name of the main protagonist in the games:
Sly Cooper and the Thievius Raccoonus
Band of Thieves
Honor Among Thieves