Major Seventh (Maj7)

Root + major third + major seventh

Prove it — just do the practice exercise.
CMaj7 Shell Voicing
C (R)E (3)B (7)
A Maj7 shell voicing consists of 3 notes:

Root — Determines the chord letter
Major 3rd — 4 semitones above the root
Major 7th — 11 semitones above the root

Example: Cmaj7 = C + E + B