D = Dual. meaning it has separate mechanicals controlling intake(1) and exhaust(2) valves, hence, "dual"OH = overhead. meaning the mechanicals controlling the valves are "over" the engine head. they are located closer to the actual parts they're controlling. hence, less distance the force has to travel through the mechanicals.C = Cams. A part that controls the opening and closing of the valvesIn another words, DOHC = "There are two parts that control the valves (cams) located right over the head of my engine."DOHC doesn't always necessarily mean it's better than other designs; i.e. OHV (overhead valve: cam is located farther away from the valves that it controls) or SOHC (single: single cam does both duties, intake and exhaust)and it doesn't always mean it has a "variabale" (another can of worms) technology. it all depends on the application and individual design. But when all else are equal, DOHC design provides more flexible/efficient way for engine to breathe more.