"The Sanskrit word bandha means to hold, bind, or lock. Yoga Bandhas refer to four internal locks - a technique to contract and release key muscles of the abdomen or sphincters in the neck or pelvic floor. Doing so strengthens, compresses, or redirects the flow of prana - the vital breath - to a desired region. Bandhas must be performed in conjunction with pranayama, meditation, or yoga breathing. "
The Great Lock: Maha Bandha