Mediant

In music, the mediant is the third degree of the diatonic scale. For example, in the C major scale (white keys on a piano), the mediant is the note E; and the mediant chord uses the notes E, G, and B. In music theory, the mediant chord is symbolized with the Roman numeral III if major or iii if minor.

"Mediant" also refers to a relationship of musical keys. For example, relative to the key of C major, the key of E major is the mediant. Modulation (changes of key) to the mediant are relatively rare, compared with, say, modulation into the dominant.