Classical yoga is a dualistic philosophy where the universe is envisioned as a combination of perceivable material reality (prakriti) and non-perceivable, non-material laws and principles of nature (purusha). Prakriti is everything that has changed, can change, and is subject to cause and effect. Purusha is the unchanging and uncaused Universal Principle.
In yoga, purusha also references the true Self -- the realization of which is a goal of yoga practice as defined in "The Yoga Sutras of Patanjali." It is also the ultimate goal of all Vedic practices and Vedantic philosophy, examination and inquiry.
In Hinduism, purusha is a very complex term and has diverse meanings. There is no consensus among different schools of Hinduism on the precise definition of purusha, and it is left to each school and individual to reach their own conclusions.
In the Upanishads, the concept of purusha evolved to denote an abstract essence of Self and Spirit, as well as the eternal, indestructible, all-pervasive Universal Principle. Although there are a variety of views held in different schools of Hinduism about the definition, scope and nature of purusha, many of them agree that it is what connects everything and everyone.