Triads, 7th Chords, Lead-sheet Symbols
Dr. B Music Theory

Triad

The most common chords are triad. It's a 3 notes chord.

triad = tertial types/sonorities:

Lead sheet symbols

The 1 is called the root, the 3 is called the 3rd and the 5 is called the 5th.

The root of the chord is always write in uppercase letter. For exemple:

Seventh Chord

Using 4 notes. The interval between root and top note is a seven.