Mastering is the final step before an album can be released. The mastering process is a method to maximize the potential of a mix on various different audio setups. The process can be entirely different depending on the format that you wish to use to distribute your music. Such as CD, Vinyl or multiple digital formats.

DDP file for CD pressing
16bit mp3 mastering
16bit WAV mastering for CD
16bit WAV mastering for Itunes, youtube, spotify 
24bit WAV mastering for Vinyl