to define - DOHC = "Dual overhead cams"
to define - i-VTEC = "intelligent valve timing and lift electronic control"
to explain in english - DOHC = there are four chambers in your car (or six, if you have a v6) in which you have gas exploding to push pistons that make your car move. each of these four chambers have valves that let air in and out. Dual overhead cams means you have four holes for each chamber - two to let air in, two to let air out. having these pairs of holes for each of these gas-exploding chambers makes your car run more efficiently per amount of gas. still feel like i'm talking greek?
http://auto.howstuffworks.com/engine.htm http://auto.howstuffworks.com/question562.htm