The term for observing silence is mauna in Sanskrit. Various yogic and tantric texts lay great importance on observing silence. The talkative nature of the human mind is best revealed in silence. Quietude of the speech is paramount to attain complete quiescence of the mind. The finest meditation is the act of staying in a state of awareness, of quietude.
Besides sitting down and meditating, yogic scriptures outline many other activities that can help any meditator achieve that quietude and understand meditation in its truest sense. One such practice is the practice of observing silence. You can think of it as a fast from speaking.
As part of the practice of silence, you need to start with small periods first. The shortest being at least one straight stretch of twenty four hours. If you are merely observing silence of the speech by refraining from speaking, you are only fifty percent there. The practice involves observing complete silence; that means, not holding any type of conversation. Carefully examine the chart below:
For instance, you undertake the practice of observing silence for forty eight hours. During that time, if you make any verbal comments, the impact is red and huge; you need to restart the practice. If you end up reading a newspaper during those forty eight hours, the quality of your practice comes down by five percent (see the weightage column); you can still continue because it is a "green" mistake.
During your period of silence, you can at the most take one book at the beginning. But ideally, you should just be in a room in your own company. If you end up sleeping for eighteen out of twenty four hours just because you can or because you have nothing else to do, it is wasting your time; after all, we are not observing sleep but silence. The more mindful and alert you are, the better your practice. When in complete silence, you will start to become aware of the talkative nature of your mind. You will begin to see how mind is restless like the monkey that cannot stay on any branch longer than a few seconds.
Initially, your ability to meditate is going to retard while observing silence. You are likely to experience a certain restlessness as well. You need not be alarmed. It is only natural. With persistence and patience, a quietude starts to dawn. And that is going to get you ready for good meditation. Observing silence is comparable to preparing a fertile ground to sow the seeds of meditation. Awhile ago I wrote on the types of conversations the human mind is always holding; you may want to read up on that here.
Please know this: the practice of observing silence is absolutely critical for the seeker desiring to experience a state of superconsciousness. When you are enjoying yourself, listening to your iPod, the external noise seems to subside automatically; the music in your ears makes the outside sound almost immaterial. Similarly, when you are able to channelize internal noise, it transforms into music. And when you start to hear internal music, everything offered to you in the external world almost ceases to matter. Anahata nada, unstruck sound, manifests itself in its full glory in that quiescent stream. I say this from my first-hand experience.