While according to the definition, every inversion of a chord is a voicing and every voicing is an inversion, here on chord-book.com the 2 terms have their strict meaning.
Here are our defintions of each :
Any inversion/voicing of a chord which spans less than an octave (a major seventh or less). That definition still applies even if the original chord spans an octave or more.
Thus, E-G-C is an inversion of Cmaj (C-E-G), and Csus6 (C-F-G-A) is an inversion of Fadd9 (F-A-C-G).
Any inversion/voicing of a chord which spans at least an octave. That definition applies even if the original chord spans less than an octave.
Thus, E-G-C-E is a voicing of Cmaj (C-E-G), and Fadd9 (F-A-C-G) is a voicing of Csus6 (C-F-G-A).
CHORDS WITH MISSING NOTES ARE NOT VOICINGS OF THE ORIGINAL CHORD! They will be listed in chord choices instead or appearing as inversions/voicings.
I understand certain instruments, like mallets for example, can hardly play more than 4 notes at the same time, hence chords with missing notes tend to be refered to as "voicings" by those who play them,
but as per the strict definition, a voicing of a chord must contain EVERY pitch of the original chord, no missing ones, no added ones, no altered ones. The voicing is how the notes are placed, not what notes are chosen.