Extracted from Wikipedia:
Purusha (Sanskrit puruṣa पुरुष) is a complex concept whose meaning evolved in Vedic and Upanishadic times. Depending on source and historical timeline, it means the cosmic being or self, consciousness, and universal principle. Author Steven Rosen says, “The Bhagavata Purana and the Mahabharata boldly proclaim Vishnu as ultimate Purusha described in Purusha Sukta prayer”. According to Indologist W. Norman Brown, “The verses of Purusha Sukta are definitely a reference to Vishnu, who, through his three steps, is all pervading (i.e. he spreads in all directions)”.
In early Vedas, Purusha was a cosmic being whose sacrifice by the gods created all life. This was one of many creation theories discussed in the Vedas.
In the Upanishads, the Purusha concept refers to abstract essence of the Self, Spirit and the Universal Principle that is eternal, indestructible, without form and is all pervasive. The Purusha concept is explained with the concept of Prakrti in the Upanishads. The Universe is envisioned in these ancient Sanskrit texts as a combination of the perceivable material reality and non-perceivable, non-material laws and principles of nature. Material reality (or Prakrti) is everything that has changed, can change and is subject to cause and effect. Purusha is the Universal principle that is unchanging, uncaused but is present everywhere and the reason why Prakrti changes, transforms and transcends all of the time and which is why there is cause and effect. In the RigVeda, “[t]his Puruṣa is all that yet hath been and all that is to be” (पुरुष एवेदं सर्वं यद भूतं यच्च भव्यम|). Purusha is what connects everything and everyone according to the various schools of Hinduism.
There is a diversity of views within various schools of Hinduism about the definition, scope and nature of Purusha.
Definition and description
Purusha is a complex concept, whose meaning has diversified over time in the philosophical traditions now called as Hinduism. During the Vedic period, Purusha concept was one of several theories offered for the creation of universe. Purusa, in Rigveda, was described as a being, who becomes a sacrificial victim of gods, and whose sacrifice creates all life forms including human beings.
In the Upanishads and later texts of Hindu philosophy, the Purusha concept moved away from the Vedic definition of Purusha and was no longer a person, cosmic man or entity. Instead, the concept flowered into a more complex abstraction.
Splendid and without a bodily form is this Purusha, without and within, unborn, without life breath and without mind, higher than the supreme element. From him are born life breath and mind. He is the soul of all beings.
— Munduka Upanishad, (Translated by Klaus Klostermair)
Both Samkhya and Yoga schools of Hinduism state that there are two ultimate realities whose interaction accounts for all experiences and universe – Prakrti (matter) and Purusha (spirit). In other words, the universe is envisioned as a combination of perceivable material reality and non-perceivable, non-material laws and principles of nature. Material reality, or Prakrti, is everything that has changed, can change and is subject to cause and effect. Universal principle, or Purusha, is that which is unchanging (aksara) and is uncaused. The animating causes, fields and principles of nature is Purusha in Hindu philosophy. Hinduism refers to Purusha as the soul of the universe, the universal spirit present everywhere, in everything and everyone, all the times. Purusha is Universal Principle that is eternal, indestructible, without form and all pervasive. It is Purusha in the form of nature’s laws and principles that operate in the background to regulate, guide and direct change, evolution, cause and effect. It is Purusha, in Hindu concept of existence, that breathes life into matter, is the source of all consciousness, one that creates oneness in all life forms, in all of humanity, and the essence of Self. It is Purusha, according to Hinduism, why the universe operates, is dynamic and evolves, as against being static.
Both Samkhya and Yoga school holds that the path to moksha (release, Self-realization) includes the realization of Purusha.