What is the definition of "maslaha" (public interest) and what are the conditions for using it as a basis for legal argumentation?

The acceptable maslahah (public interest) according to scholars is the maslahah mursalah, meaning that which has not been restricted by the Lawgiver, neither by affirmation nor by nullification. It is a valid proof according to Imam Malik and those who agreed with him, because the Rightly Guided Caliphs and the righteous predecessors acted upon it, such as the compilation of the Noble Qur'an, Abu Bakr's appointment of Umar, and Uthman's instituting of the first call to prayer for Friday.

The maslahah mursalah applies to necessities (daruriyyat), needs (hajiyyat), and embellishments (tahsiniyyat), provided that it does not contradict a textual evidence from Islamic law, does not add a new act of worship, a pillar, or a condition, that the achievement of the benefit through it is certain or highly probable, and that the ruling built upon it is general for the entire Ummah.