30 Ajza (Para) Set of the Quran

The division of the Qur'aan into 30 parts (ajza/paras) is not a divinely ordained division. The Prophet and the sahaba did not do it. It originated in Iraq in the second century of the Hijrah in the time of the tabi tabi'oon. It was done in early Islam to facilitate reading the Qur'aan in one month. Division into 30 parts (ajza) meant one part can be read each day so that one could complete reading the Qur'an in one month (30 days). The surahs on the other hand, are divinely ordained sections/divisions of the Qur'aan. 

In arabic it is called juz = singular, Ajza= plural. In the Indian subcontinent these divisions are referred to Paras/Siparahs.