We have seen that major and minor chords are made up of three notes, the 1st note (root), the 3rd note and the 5th note.
Chords are usually constructed by playing the root note as the lowest note of the chord, and then have the 3rd and the 5th notes stacked on top of this. For example, when playing a C major chord, the note C would usually be the bass note.
However, the three different notes included in each triad can be placed in a different order to become what is called a triad inversion.
A first inversion occurs when the 3rd becomes the bottom note, the 5th is next, and the root is at the top.
A second inversion occurs when the 5th is at the bottom, the 1st is next, and the 3rd is at the top.
These inversions are used as alternative ways of playing a triad, and as such have a slightly different "motion" to the root position triad, but are still in the same key. They are basically different voicings of the same chord.