Thanks Darrell. I've heard of it but not something I've got into studying yet.
What I did pick-up from the video is that an interval is measured by the number of notes between two notes, including both notes. I was intuitively thinking that the interval would be the number of notes, excluding the first note. That is why A to C is a third.
And then the minor or major is determined by looking at the end note in the major scale of the first note. In this case of A to C it is a minor third since in the A major scale the C note is a C#. Therefore in this interval it is flattened by a semi-tone, which makes it a minor.
So A to B would be a major second?
Lots to learn

Meanwhile, didn't pick up anything in this to give me a pointer as to what chords I should be playing if I want to start playing my A minor pentatonic (at the 5th fret as instructed in BC stage 7) over a chord progression. Maybe I should be playing Am and C? Would it work to play other chords in the C maj scale, such as Dm and Em? I assume that would work if I was playing the C maj scale, but not sure about this given I am using a minor pentatonic.
And this has now become a hijack, I think ...
Darn, I did it again ...