The concept of Maat was central to Ancient Egyptian thought. Often simply translated as justice, Maat actually expresses the proper order of the universe, right thinking, correct action and the regulation of time and space. It has hints of social propriety, the pyramidical nature of interaction between people, the respect that is due to a father, the duties one should show to a son. It encompassed the majesty of the Pharaoh and the loyalty that is owed to him by a subject, as well as his duty to protect and nurture his people. There is no doubt that pharaohs believed that they ruled under the auspices of Maat.
Maat was personified as a goddess from earliest times. A daughter of Ra, Maat came into existence as the cosmos was born. She can be thought of as a female equivalent to wise Thoth; like him, a regulator of the seasons who keeps the stars in their proper courses. She is usually portrayed wearing an ostrich feather on her head, or simply as the feather itself. It is in this form that she is central to the judgement of the dead. It is she who is set in the balance against the heart of the deceased to measure whether he was “justified” in life or not. The place of judgement in the underworld, where Osiris sits, is known as the Hall of Maat.
Though there are few temples to Maat she was widely honoured, so much so that the chief minister of the Pharaoh was given the title High Priest of Maat.
Source: Chronicles of Ancient Egypt by Jonathan Dee