Methods of house division that associate the ascendant with the cusp of the 1st house, the MC with the cusp of the 10th house, the descendant with the cusp of the 7th house and the IC with the cusp of the 4th house, and then seek an equal division (of time or space) within those quadrants. The equal house system is not a quadrant system, and so the MC does not necessarily denote the cusp of the 10th house.

The division of the celestial sphere by the horizon and meridian to give four quarters between each of the four angles.

The person asking the question in a horary chart.

The thing asked about in a horary chart.