A transmission that provides power directly to all four wheels of a motor vehicle(noun)
A motor vehicle with a four-wheel drive transmission system(noun)
WordNet. Princeton University. 2010.
Use "4wd" in a sentence
"There was a small hill I was unable to drive up in 4wd with normal all seasons."
"Incidentally, if you go to the preserve, don't attempt it on your own even if you have 4wd, which is probably useful."
"I don't care what they do to their vehicle, but I have to laugh when I tow them somewhere with my normal 4wd S-10 because they bottomed out and broke the oil pan!"