When the lowest note in a chord, is the same as the name of the chord (for example, the C Major chord, shown above, has C as the lowest note) then the chord is said to be in 'Root Position' ( just as a root is the lowest part of a tree)
As there are three different notes in all Major chords, they can be played in any order, and still be a chord.
For example, the C chord above, consists of C, E, and G in that order.
It would still be a C major chord, if you changed the order of the notes, and played, E, C, and G, or G, C, and E
This is known as inverting the order, so any order you play the notes in, other than Root Position, is called an Inversion
So, C E G is called Root Position
E G C is called First Inversion
G C E is called Second Inversion
As pictures and sound speak louder than words, you can see and hear the most common Major chords, and their inversions by clicking anywhere on the keyboard below.