it refers to a yoga technique used in some prāṇāyāma. After having exhaled all the air out of the longs, one has to pull its abdomen under the rib cage by taking a false inhale while withholding breath. When one feels the need to inhale, one must release first the abdomen completely and then inhale.
Uḍḍiyāna Bandha
it refers to a yoga technique used in some prāṇāyāma.