This example comes from the Theory section on augmented and diminished triads.

There are 4 fundamental triad types:

Major Triad: 1st - 3rd - 5th of the major scale
Minor Triad: 1st - b3rd - 5th of the major scale (or 1st 3rd 5th of the minor scale)
Augmented Triad: 1st - 3rd - #5th of the major scale
Diminished Triad: 1st - b3rd - b5th of the major scale (or 1st 3rd b5th of the minor scale)

Here we play these 4 basic chord triads for D:

D major scale: D - E - F# - G - A - B - C# - D

D Major Triad: D - F# - A This is the first chord in the ActionTab. The chord strums through the 3 triad notes in this order: D - A - D - F# (from lowest to highest string).

D Minor Triad: D - F - A This is the second chord in the ActionTab. The chord strums through the 3 triad notes in this order: D - A - D - F (from lowest to highest string).

D aug Triad: D - F# - A# This is the third chord in the ActionTab. The chord strums through the 3 triad notes in this order: D - A# - D - F# (from lowest to highest string).

D dim Triad: D - F - Ab This is the last chord in the ActionTab. The chord strums through the 3 triad notes in this order: D - Ab - D - F (from lowest to highest string).

Major and Minor Triads are by far the most common triad types. However, augmented and diminished chords are important too. They often appear in jazz music for example. Because they aren't as harmonically 'stable' as the major or minor triads they have a dissonant sound. This is often used for creating tension in music. Listening to the chords in this ActionTab you can see how those augmented and diminished chords cause that kind of horror movie tension!

Remember that all other chords are extensions or adaptations of these fundamental 4 triad types, so familiarity with them is very useful!