DDR stands for double data rate, which means technically your RAM doesn't run at its advertised speed in megahertz, but rather operates as if it was. For every clock (cycle), DDR RAM transfers data twice. Some people prefer to use megatransfers, or million transfers per second (MT/s) when talking about RAM speeds for this reason, as that's more accurate.
If you're a stickler for semantics, this matters. Otherwise it's basically fine and well-understood both ways.