"Kumbhaka" means breath retention. In AYP, this practice is used together with Yoni Mudra.
Yoni Mudra Kumbhaka is an advanced technique that should be undertaken only after more basic practices (meditation, spinal breathing pranayama etc.) are mastered.
Yoni Mudra Kumbhaka consists in placing the tips of our two index fingers close to the outer corners of our closed eyes against the lower lids and gently pushing the eyes up and to the center in the direction of the point between the eyebrows. Spinal breathing is done from the perineum to third eye, the nostrils are closed. The tongue is raised to block air from passing through and the breath is gently held.