Uḍḍīyana Bandha (Sanskrit) is the abdominal bandha described and employed in hatha yoga. It involves, after having exhaled all the air out, pulling the abdomen under the rib cage by taking a false inhale while holding the breath and then release the abdomen after a pause. The process is repeated many times before letting the air into the lungs, resuming normal breath.
References
Uddiyana bandha Wikipedia(Text) CC BY-SA