Kumbhaka Terminology Often Used

Puraka - Inhalation
Rechaka - Exhalation
Kumbhaka - Breath retention

Kumbhaka means a pot which can be full or empty. Kumbhaka is of two types. It is either a pause between an 'In' and an 'Out' breath, or between an 'Out' and an 'In' breath. It is the art of retaining the breath in a state of suspense.
Vrtti means action, movement, a course of conduct or method.

There are two types of vrtti pranayamas: Samavrtti and Visamavrtti. It is the former if the length of time in each inhalation, exhalation and retention of breath is the same. And it is the latter if the length is altered and varied.

Samvrtti Pranayama
Sama means equal, identical or in the same manner. In samavrtti pranayama an attempt is made to achieve uniformity in the duration of all the four processes of breathing, namely, inhalation (puraka), retention (antara kumbhaka), exhalation (rechaka) and retention (bahya kumbhaka). If the duration of puraka is say, five seconds or ten seconds, it should be the same in rechaka and kumbhakas.

Viumavrtti Pranayama
Visama means irregular. Visamavrtti Pranayama is so-called because the duration of puraka, antara kumbhaka, rechaka and bahya kumbhaka are varied. This leads to an interrupted rhythm, and the difference in ration creates difficulty and danger for the pupil, unless they are gifted with strong nerves, and good lungs.