What does 4/0 and 4/4 mean?

4/0 and 4/4 are common printing terminology terms and basically means single or double sided printing. 4/0 refers to printing 4 colors on one side of the paper and 0 colors on the other side of the paper. 4/4 means 4 colors printed on both sides of the paper. The four colors in process color printing are CMYK, (Cyan, Magenta, Yellow and Key - which is black.)