Hatha Yoga
This is a style of yoga that is mainly associated with postures because the first text that we know of that goes into depth about the poses that are yoga is the Hatha Yoga Pradipaka. The world Hatha means sun-moon (ha-sun tha-moon). In essence, the idea of union is to bring life in contact with non-life or vice versa through our practice. This is a dualistic repeat of the word yoga. Only with the word yoga, we are trying to unite ourselves in the world. Sometimes what we find in ourselves to be static and stagnant is lifeless compared to that which is around us and other times we find what is lifeless and stagnant. Other times it does work the other way around as we bring life to the soil, water, or mountains.
Going into the idea as the sun-moon relation going into posture. Many teachers jump onto this idea of having postures being in a balance of stillness and energy. I agree with this and I find that poses need more than that. We need to resurrect ourselves, or at least much of ourselves, or awaken ourselves from slumber with poise, grace, and strength to life!