In music, a major seventh chord is a seventh chord where the “third” note is a major third above the root, and the “seventh” note is a major seventh above the root (a fifth above the third note). The major seventh chord, sometimes also called a Delta chord, can be written as maj7, M7, Δ, ⑦, 7+, etc. In the case where the seventh note is a minor seventh above the root, it is instead called a dominant seventh chord.
Any scale that contains all the chord tones of a chord can be used for improvisation over that chord. The following scales contain all the Major chord tones (1,3,5,7)