A chord may be defined as a combination of three or more notes played simultaneously. Every chord is based on a specific formula which relates back to the major scale after which it is named.
All chords are based upon or derived from the four basic chord types i.e., major, minor, diminished and augmented. These chords consist only of the 1st, 3rd and 5th notes of the major scale.
Each chord type is derived from the major scale after which it is named.
For example, C major is derived from the C major scale.
C minor is derived from the C major scale.
F diminished is derived from the F major scale.
Bb augmented is derived from the Bb major scale.