DDR 2 / 3 / 4 / 5 what does it mean?

Ok so i'm new to pc gaming but planning to build my own pc at the start of next year and i keep hearing and seeing this DDR stuff. So what exactly does it mean ? I'm guessing the higher the number the faster it is as i've seen it on gpu's and ram i think so if anyone could explain this to me it would be much appreciated.

http://www.crucial.com/kb/answer.aspx?qid=3773

it's hard to explain

https://en.wikipedia.org/wiki/DDR_SDRAM#Variations

http://www.makeuseof.com/tag/difference-ddr2-ddr3-ram-technology-explained/

so readup and enjoy!

also, the CPU standard is ddr3 and the GPU standard is gddr5 (g for graphic I believe)

intel is pushing ddr4 for cpus around 2014.

as for gddr4, they just kinda skipped it like the Nvidia 3xx series

ok, thanks for the links. 

I think i understand all this better now and it's starting to make some sense