30 Ajza (Para) Set of the Quran

The division of the Qur'aan into 30 parts is not a divinely ordained division. The Prophet and his companions (sahaba) did not do it. It originated in Iraq in the second century of the Hijrah in the time of the tabi-tabi'oon (2 generations after the sahaba). 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 divisions of the Qur'aan. 

In Arabic one part is called a juz = singular, Ajza= plural. In the Indian subcontinent these divisions are referred to paras/siparahs.