Joe Bonamassa LOVES Thirds!
So let's take an example. At 0:47 that very first riff he's talking about starts like this: x 10 x x 11 x but then he bends the 11th fret up a semitone. Well, what's he starting with? That's a G on the 5th string, and a Bb on the 2nd string... that's a G minor third. Then, he bends the Bb up to a B, creating a G major third. Voila - thirds in action! Sounds awesome!
Okay, let's do one more. In Joe's Trick #3, he shows a really cool way of producing a sound on a standard tuned guitar that sounds like the guitar is actually tuned down lower than it is. He calls it a low V inversion, but you could also call this an inverted third.
Take a look: At 6:15 he does the first one, and the notes he is using are 3 x 2 x x x. Or, G and E. Well, we're talking about inverted thirds, so that means that E is our root note, despite being the higher of the two notes, which means we're dealing with an inverted E minor third.
Fancy name for a very sweet sound.
Regardless of what you call it, learning how to master thirds in your playing is a terrific way of adding a lot of character to your solos and riffs. In my course Secrets of Tasty Riffs & Solos, I didn't go in the same direction Joe has here, however that is the beauty of thirds - there are literally endless variations and directions you can go with them. The really key thing is to learn to recognize them on the fretboard, and then begin experimenting with them.
We do both in Secrets of Tasty Riffs & Solos.