Rabb is an Arabic word meaning Lord, Sustainer, Cherisher, Master, which in Islamic context refers to Allah. In the Qur'an, rabb is one of the usual names of God.
Pre-Islamic Arabia probably applied this term to its gods or to some of them. In this sense the word corresponds to the terms like Ba'al, Adonis, etc. in the Northwestern Semitic languages, where rabb means "much, great" A. Jeffery, The foreign vocabulary of the Qur'an, Baroda 1938, 136-7 .
In an older surah, Allah is called the "Lord of this House" (106:3). Similarly, al-Lat bore the epithet al-Rabba.