A 4/3 chord is a triad in second inversion, meaning that the fifth of the chord is in the bass. It is often represented by Roman numerals with a slash and numbers indicating the intervals above the bass note.
Root position: A triad where the root note is in the bass.
First inversion: A triad where the third of the chord is in the bass.
Figured bass notation: A system of shorthand symbols used to indicate chords and their inversions.