What does 4c / 4-color / 4/4-color and CMYK mean?

4c or 4-color means nothing other than "CMYK" CMYK is the abbreviation for the 4 color components cyan, magenta, yellow and key ( Black). These serve as the basis for all modern printing processes for creating colored images. Almost all printing colors can be mixed from these basic colors. When creating print files, it is imperative that they be created in CMYK mode. The RGB mode is only suitable for display on the monitor and is not suitable for printing, otherwise the colors will be displayed differently in the print.

For special house or company colors, so-called HKS and Pantone colors (“special colors”) are used, which guarantee color fastness. The special colors also include gold, silver and neon tones. Special colors must be specifically requested.

By the way, 4/4-color means nothing other than that your printed matter is printed on both sides with CMYK. (Double-sided "full color" printing.)