Prāṇa is the Sanskrit word that describes the vital life force or primal energy manifested in all aspects of the Universe. This cosmic energy radiates from the sun and is absorbed by life here on earth. We also absorb prāṇa from the air we breathe and the food we eat. In this sense it is analogous to "Qi" in traditional Chinese culture. It is the active principle in all living things, and can also signify more specifically "breath" or "air."
Prāṇāyāma is a compound of two Sanskrit words. It is often broken down to "Prāṇa-yāma" meaning the control of the breath or life-force; however it is more accurately translated as "Prāṇa-ayāma" referring to the extension or expansion of the breath and its connection to this primal energy. It is the ancient art and science of "yogic breathing" through which the practitioner learns to control, expand, and channel their vital energy by gradually training one's ability to hold and lengthen the inhalation and exhalation using various techniques.
There are formal exercises that can be practiced daily which will encourage control over the breath, subsequently resulting in the expansion of one's energy over time. However, without proper guidance and instruction from a qualified teacher, the exercise of restraining the breath can in certain cases be harmful, and so the practice of prāṇāyāma should never be learned from a book, video, CD, or over the internet.
The mind and the breath are said to arise from the same Source, and so to learn specific methods for controlling the breath can lead directly back to this Source. Thus, gaining control over the breath is a means to achieve mastery over the mind. The great Indian Sage, Ramana Maharishi says in Maha Yoga: "prāṇāyāma is of two kinds: one of controlling and regulating the breath and the other of simply watching the breath." Similarly, in the book, Day-By-Day with Bhagavan, he is recorded as stating: "seekers are advised to watch their breathing, since such watching will naturally and as a matter of course lead to the cessation of thought and bring the mind under control." In the Ashtanga Yoga system of Sri K Pattabhi Jois the breath is under constant observation. With daily practice it becomes steady, smooth and equal, and consequently, controlled. By this definition the practice integrates a form of prāṇāyāma, as its regulation is attained by watching its movements.
Prāṇa as the unlimited life force is found all around us. Everything we interact with affects our prāṇa in some way or other. Some activities or substances give us energy, while others drain us of it. One thing I love about being with my son Jediah is to see this life force radiating in abundance through him in the form of pure joy. His curiosity and playfulness seems to be never ending. During those times when I can be completely present to this unadulterated energy through my attentiveness to him, I am aware of precious moments where I am a direct witness to the miracle of this prāṇa expressing itself uninhibited.
I often think, wouldn't it be incredible to be completely aware of this pure cosmic life force as it expresses itself through each and every person, and even beyond that - as it exists in all things. I think this may be what Guruji meant when he talked about pratyahara (sense withdrawal) as a method for "Seeing God in everything." It is the natural evolution of prāṇāyāma as the expansion of our ability to observe all around us the miracle of life, which can only be called Divine.