Purusha [also: Purusa] is that which is existent in vibratory creation, and also existent beyond it.
The Supreme Being (Purusha) manifests Itself in and as Prakriti (Cosmic Nature) and the human body (the "little Prakriti"), It remains simultaneously transcendent, "beyond, or different from" Its manifestation.
Purusha is considered as the first concept of Sankhya philosophy. Pur means 'city'. Sheta means 'dwelling, living, existing'. Purusha is that pure Consciousness that exists, lives, dwells in the city of senses. The body is a city of senses. Purusha can be called pure Consciousness. Purusha is the universal principle that is unchanging, uncaused and present everywhere. Pususha is the witness in which everything is occurring. This conscious energy of Purusha is related to Shiva, the male energy. [Sankaralingam]
The Spirit beyond creation, as God, and the Spirit in creation, as Kutastha, are both called Purusha. The Transcendental Intelligence existing beyond creation is Para-Purusha; its intelligence reflected in creation is Kutastha-Purusha. Purusha beyond creation is also called Ishvara, or God the Creator. The Purusha in creation is called Kutastha Chaitanya, or immutable universal intelligence.
The Gita: III:19
Know that both Purusha and Prakriti are beginningless; and know also that all modifications and qualities (gunas) are born of Prakriti.
The Gita III:20:
In the creation of the effect (the body) and the instrument (the senses), Prakriti is spoken of as the cause; in the experience of joy and sorrow, Purusha is said to be the cause.