Pratyahara is derived from the Sanskrit roots prati, meaning "away" or "against," and ahara, meaning "nourishment" or "food." Therefore, the whole word denotes a withdrawal from what nourishes the senses.
Pratyahara comes after the earlier limbs of yoga because, before the senses are turned inwards the mind must be purified and calmed by yama, niyama and pranayama. When the senses are withdrawn, they become absorbed by the mind itself, rather than engaging the mind with the external environment. It is said that this allows the practitioner to experience the true inner Self.
It takes years to develop a practice of pratyahara. But, once it is established, it allows the mind to become peaceful so that good concentration and meditation can be developed. It is said that once someone has mastered pratyahara, they will never again experience distraction or need to withdraw from the world in order to meditate. They will simply be able to turn the senses inward. As such, pratyahara gives the practitioner power.
Pratyahara can be practiced during pranayama, bringing the focus away from external stimuli and onto the breath. It can also be developed through the first stages of yoga nidra
where all the senses are withdrawn, except for hearing, and focus is shifted only to the instructions of guided meditation.