Question: what is the difference between a major 7th chord?
Answer: What's the difference between 7th and major 7th chords? "7" means a minor (smaller) 7th, 10 semitones above the root. "maj7" means a major (larger) 7th, 11 semitones above the root. The smaller one is more common, hence the default "7" in shorthand chord symbol terminology.