Watch the Changing Voicings online guitar lesson by Vicki Genfan from Acoustic Rhythm Survival Guide
A 'voicing' refers to the order of the notes in a chord. Each voicing has a particular sound. You may chose a certain voicing for a chord because you simply like the way it sounds, or maybe you are trying to pick a melody out on a particular string (your high E string for example) and so you will be looking for chord forms that give you access to those notes.
You might prefer voicings that have 'close' more 'open' voicings where the notes are far apart, and the effect is more peaceful or calm.
If you are playing as a solo guitarist or with just a singer, you might want to chose voicings that have the root of your chords on one of the low strings (Low E, A or D). However, if you're in a band or even just playing with another guitarist or instrument, then you have a lot more freedom to explore new voicings.
In this way you can add some great color tones and textures to the music, without being tied to any bass notes and without getting in the way of your bass player or fellow musicians.
The possibilities are indeed endless, when it comes to finding voicings for a chord and there are many chord books that can supply you with a great wealth of voicings to choose from if you don't want to find them all by yourself!