Nauli is one of the Kriyas (1) or Shatkarma (cleaning exercises) from Yoga. The exercise is to serve the cleaning of the abdominal region – digesting organs, small intestine and is based on a massage of the internal belly organs by a circular movement of the abdominal muscles.
Nauli is an exercise of the classical Hatha Yoga but is not taught often in yoga schools. Nauli is considered as a difficult exercise, which can be learned only with perseverance and patience. There are four different variations, which are gradually learned one after another:
madhyana nauli: the isolated contraction of the central muscles of the abdominis
vama nauli: (2) the isolated contraction of the left part of the central muscles of the abdomen
daksina nauli: the isolated contraction of the right part of the central muscles of the abdomen
nauli kriya: the circular movement of the central muscles of the abdomen
In yoga, Nauli generally recommended for the recovery of constipation. The exercise may clean the small intestine and eliminate digesting problems.
Nauli is generally done standing but it is possible to do it in other position like lotus, whereby the trunk is bent forward and is supported by the hands at the thighs. After a complete breath out the entire belly is strongly brought in and then the middle belly muscle is contracted and moved in a circle.
Definition courtesy Wikipedia.