What is Asana Yoga?
Asana is the physical practice of yoga poses. What most of us call yoga (as in, "Bye honey, I'm off to my yoga class") could more specifically be called asana since the word yoga also encompasses pranayama, meditation, and five other "limbs". In addition to referring broadly to the physical aspect of yoga, asana can also be used to describe a single pose (as in, "Handstand is an asana that is really hard for me.").
The History of Asana
It's significant to note that asana is the Sanskrit word for posture or seat. The first yoga asanas, as interpreted from the archeological record and primary source materials, were most probably seated positions for meditation. It is not until fairly recently in yoga's history (and with the influence of the Western physical culture movement) that asana developed such a wide array of poses and became the most widely practiced aspect of yoga. Understanding this goes a long way toward accepting that asana is not a static practice enshrined through the millennia. Rather, it is constantly evolving. A pose invented last week isn't less legitimate than one from the 1940s or the 16th century.
The Sanskrit Names for Poses
You may have noticed that asana is used as a suffix in the Sanskrit names for yoga poses: trikonasana, virabhadrasana, and eka pada rajakapotasana, for example.
Knowing this and a few other Sanskrit terms can help you unravel these complicated names. For instance, eka pada means one footed, so in these poses, you can expect that one foot will be doing something different from the other. Parsva means side (usually a pose facing one side), parivrtta means turned (usually a twisted version of a pose), and so on.