(Sanskrit प्रत्याहार) Literally, "withdrawl, drawing back, retreat."
In yoga, the fifth of the eight steps of Ashtanga Yoga (Raja Yoga), which is to withdraw the consciousness from the senses so attention can be fully directed within.
"He who has gained Pratyahara (withdrawing the senses from the objects) will have a good concentration. You will have to march in the spiritual path step by step, stage by stage. Lay the foundation of Yama, Niyama, Asana, Pranayama and Pratyahara to start with. The super-structure of Dharana and Dhyana will be successful only then." —Swami Sivananda
"If you want Samadhi, you must know well the process of Dhyana. If you want Dhyana, you must know accurately the method of Dharana. If you want Dharana, you must know perfectly the method of Pratyahara. If you want Pratyahara, you must know Pranayama. If you want Pranayama you must know Asana well. Before going to the practice of Asana, you should have Yama and Niyama. There is no use of jumping into Dhyana without having the various preliminary practices." —Swami Sivananda
According to Blavatsky, this word is related to Mahapralaya, or the Great Night or great rest, which can be understood as the rest or silence of the mind.