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