I think you mean PSD, which stands for Photo Shop Document. It is the name of the file extension created when you create or edit a multi-layered image in Photoshop.
"PDS" can stand for many things. Among the most popular are as follows Public Distribution System Particularly Dangerous Situation, which is a type of tornado watch issued by the United States Storm...
Photoshop CS5 is image editing software and CS5 is version of software.
CS stands for Creative Suite, as in Adobe Photoshop Creative Suite 5.
It is simply version of this program, they counted till 8 then start with CS (9), now is CS5
CMYK stands for Cyan-Magenta-Yellow-BlacK