ركوع
Rukūʿ
The bow in the salah; a single unit of the prayer, with its bow, is a rakʿah.
What it means
Rukūʿ is the bow in the salah, made by bending from the standing position with the hands on the knees while praising God. Faruqi renders it as kneeling or genuflection. The singular rakʿah names one complete unit of the prayer, which contains one bow and two prostrations. The Quran commands believers to bow with those who bow (2:43) and to bow and prostrate themselves and worship their Lord (22:77). The word has given the prayer its units, and Muslims count their prayers by the number of rakʿāt. In the bow a worshipper declares the glory of his Lord, the Almighty.
Often misunderstood as
That rukūʿ is kneeling, when it is a bow made from standing.
Term and Arabic as listed in Ismail al Faruqi, Toward Islamic English (International Institute of Islamic Thought, 1995), p. 55, listed as RUKŪ‘. The definition is restated here.