Taixi, embryonic breathing, names a Daoist ideal of breath so refined and internalised that the adept is said to sustain life without depending on ordinary breathing through nose and mouth at all, drawing instead on an inner circulation of qi comparable, the tradition's own imagery holds, to the way a foetus is nourished in the womb without drawing breath through its own lungs, an image that gives the practice both its name and its conceptual centre.
The idea is attested in Daoist texts from the early medieval period onward, developing within the broader tradition of Daoist breath cultivation and internal alchemy, neidan, that treats refined control of breath and qi as central technology for the tradition's pursuit of longevity, health and, in its fullest religious framing, transcendence, positioning taixi as an advanced or idealised state within this wider cultivation framework rather than a simple beginner's breathing exercise. Classical accounts describe taixi in terms of extremely prolonged, extremely subtle breath retention and circulation, an ideal state practitioners work toward gradually through sustained cultivation rather than a technique performed in a single defined sequence the way several of the yogic pranayamas are, which is part of why taixi is generally discussed in Daoist literature as much as a described goal or attainment as a fixed, teachable procedure.