For a second I thought it would be incredibly funny to just leave this writeup blank, but then I considered my precious XP and thought better of it. A vow of silence, very basically, is usually a religious (but not necessarily so) resolution taken by a person to utter no words during a period. Reasons for such a vow vary between spiritual awakening through deep thought unbroken and untarnished by meaningless words, a sacrifice of the gift of speech in order to achieve/receive something or give penance for something one has done, and sometimes you're just being a stubborn dweeb. The length of time one spends doing this might be pre-determined, undetermined, or permanent. Monks and Buddhists living in reclusive theological studies are most commonly associated with taking the vow of silence.