What is "second inversion"

n. (context music English) a position of a chord when the fifth of the chord is the lowest note

The second inversion of a chord is when the fifth of the chord is in the bass. For example, G in the bass of a C major chord. The bass note and the root of the chord are a fourth apart which traditionally qualifies as a dissonance. There is therefore a tendency for movement and resolution. In notation form, it is referred to with a c following the chord position (For e.g., Ic. Vc or IVc) or as a chord (as in I).