Ruku' means to bend the body to bow. This bowing is one of the acts required in Islamic Prayer. Additionally, the same word denotes a certain unit in the Qur'an. The whole Book, for the sake of the convenience of the reader is divided into thirty parts (ajza', sing. juz'), and each juz' consists usually of sixteen ruku'.

In prayer, bowing at the waist

is the act of bowing in the Salat