Sahasrara is not a chakra, as is often believed. The chakras are within the realm of the psyche. Consciousness manifests itself at different levels, according to the predominantly active chakra. Sahasrara acts through everything and nothing simultaneously. Sahasrara is beyond the beyond (parat-param) and is also directly here.
Sahasrara is the culmination of progressive ascent through the different chakras. It is the crowning achievement of awareness. The power of the chakras does not reside in the chakras themselves but in sahasrara. The chakras are just switches. All the potential is located in sahasrara. The literal translation of the word sahasrara is a thousand. For this reason it is said to be a thousand-petalled lotus. However, even if it literally means a thousand, the word sahasrara indicates that its magnitude and importance is, in fact, unlimited. Hence sahasrara can be more appropriately described as a lotus with an infinite number of petals which are usually red or multi-colored.
Sahasrara is both formless (nirakara) and formless (akara) and is also beyond form and therefore untouched by form (nirvikara). It is shunya, or in reality, the emptiness of wholeness. It is Brahman. It’s all and nothing. What we say about sahasrara immediately limits and schematizes it, even if we say it is infinite. It transcends logic because it compares one thing to another.
Sahasrata is the totality and so what can it be compared to? It transcends every concept although it is the source of every concept. It is the fusion of prana and consciousness. Sahasrara is the culmination of yoga, the perfect union.

By Swami Satyananda Saraswati