I just watched a video about music theory and the guy in the video sounded as if there is a difference between
AMaj7 which would A C# E G
And something he called an "A major dominant seven"
Is there a difference?
Amaj7 is an A major chord with a maj7 note attached. A C# E G#. A dom7 (A7) is A major with a flat 7. A C# E G. Am7 is an A minor chord with a minor 7 attached. A C E G. Am maj7 is A minor chord with a major 7 attached. A C E G#. That's about it. Maybe post a link to the video - which sounds spurious!
We're in a morass of terminology here!
In terms of describing stand-alone chords, A major (A, C#, E) is just called A.
A7 is A, C#, E, G.
This is sometimes called a 'dominamt 7th' chord type, though it isn't being the dominant of anything at the moment. It could be the first chord of a Blues in A major. It could be the dominant 7th chord in D major (or minor). It could be II7 in G major (yes, it can include a note not in the G scale and still be 'in G major'. Latch on to that idea folks, you'll need it a lot). It could be all sorts of other things. A substitute dominant-function chord in Db major perhaps.
Amaj7 is A, C#, E, G#. The 'major' part of the name refers to the major 7th, G#.
The dominant 7th OF A major is E7. But now we're talking about what a chord DOES, not what it IS.