When you lie down, bow deeply, or kneel in a submissive position, that's prostration. Many religious rituals include various forms of prostration.
When a Catholic kneels to pray in church, or a Muslim bows his head to touch the ground during prayers, it's an act of prostration, or making yourself humble before a god or religious figure. In Hinduism, touching the feet of a guru (or teacher) is a sign of respect, and also a form of prostration. The source of this noun is the adjective prostrate, literally "lying face-down," from the Latin prosternere, "throw down."