Wikipedia
Badā' (meaning: "revealing after concealing", or "alteration in the divine will") is a Shia Islamic concept regarding God. It refers to God revealing his will about a decision, wherein the people thought his will had already been made on that issue, as the Shia believe that God has knowledge of the ultimate outcome.
Twelvers, along with other Shia sects such as the Zaydis, reject predestination. This belief is further emphasized by the Shia concept of Bada’, which states that God has not set a definite course for human history. Instead, God may alter the course of human history as is seen to be fit.
Shia Twelvers believe matters relating to the human destiny is of two kinds: definite and indefinite; God has power to change every thing which he wills and God's creativity is continuous.