or "dubs" are a reference to large wheels that can be installed on automobiles, such as cadillacs. It is a noun and a verb, just like e-mail. One might say "I have recently purchased a Cadillac and I was wondering if I could have some d's put on it?" or, in more ghetto terms, "Just bought a cadillac, throw some d's on that bitch." Another way in which the term d's can be used is, "D my car bitch." or "Could you please d up my vehicle"