Mastering, a form of audio post production, is the process of preparing and transferring recorded audio from a source containing the final mix to a data storage device, the source from which all copies will be produced.
Mastering is the term most commonly used to refer to the process of taking an audio mix and preparing it for distribution. There are several considerations in this process: unifying the sound of a record, maintaining consistency across an album, and preparing for distribution.
Traditionally, mastering is done using tools like equalization, compression, limiting and stereo enhancement. Think of mastering as the glue, varnish and polish that optimizes playback quality on all devices — from tiny iPhone speakers to massive dance club sound systems.