A single note played is termed a unison. Two notes played together (or close together) is termed an interval. Three or more notes in combination is called a chord. Chords can have any number of notes in them, but the most basic type of chord is termed a triad.

There are four types of triads commonly used:

Major triad — made up of the root, 3rd and 5th of the major scale for that key.

Minor triads — made by lowering the 3rd 1/2 step.

Diminished triads — made by lowering both the 3rd and 5th 1/2 step.

Augmented triads — made by raising the 5th 1/2 step.

Watch the short video:

By learning the 4 basic triads in all 12 keys, you automatically know and can play 48 chords! Not bad for only learning 4 variations of a triad chord.