In music theory, a major seventh is an interval that has eleven half steps 
The major seventh requires that:
- The interval must be a seventh interval (seven note names between the first and the last).
- The interval must have eleven half steps.
What does a major seventh look like?
Here is an example of a melodic major seventh (two music notes in a melody) and a harmonic major seventh (in a chord):
How to recognize a major seventh?
Rule of music theory: All intervals in a major scale starting with the tonic (degree I) are either major or perfect, and only unison, octave, fourth and fifth are perfect (the others are major).
Example with the interval G / F♯:
Let's take the G major scale to have G as the tonic:
From the rule stated above, it becomes clear that G / F♯ is a major seventh.
Inversion of the major seventh
The inversion of the major seventh is the minor second.
Here is an example of a minor second:
Musical examples of major seventh
Baba Yaga from Pictures at an Exhibition by Mussorgsky
In the introduction of The Hut on Hen's Legs (Baba Yaga) from Pictures at an Exhibition by Mussorgsky, there are major sevenths:
Interval identification game
You will find this interval in my Intervals identification game:
