"Mas" is Spanish for much, "Deuces" is latin for 2 but in the modern age has been used to symbolize the two finger peace sign hence, "deuces" for the two fingers. Usually used together as a farewell statement to close friends. Literally means, "much peace".
Speaker 1: "It been fun, see you tomorrow!"
Speaker 2: "Okay, mas deuces!"( Holds up peace sign after farewell handshake)
Speaker1: "Mas Deuces, homie." (Holds up peace sign after farewell handshake.)