Musical Theory skill
Bardic Lore is the new name of this skill, which will eventually include more than what Music Theory used to.
Musical theory is a primary skill of the bards used with their unique music based abilities.
Musical Theory is now the exclusive domain of the Bard guild, although in the past this skill was open to all.
"Music theory is basically a direct booster of other skills. Anything that deals with music or sound will probably get a bonus based on your music theory...so the higher your theory, the bigger the bonus you'll get to all your other music/sound-based abilities. This includes both normal playing and enchantes, and other sound/music-based abilities." (Dartenian)