Mastered is a term used in the music and audio industries. It is usually a song that is in or at its final stage before
mass production or sells.
A mastered song is a single stereo track that has been finalized by a mastering engineer who uses his skills, technique and gear to bring the life out of a mix.
Fatten it up, making it full and thick at the same time bringing out certain parts
in the mix. example - vocals.