What is the meaning of "yin angle and yang angle" in architecture? Which part is it?

The internal angle of a building is characterized by not exceeding 180 degrees. If it is greater than the external angle, the included angle between building components is the internal angle. For example, standing in our usual room, the angles between walls and ceilings, and between walls are angles; What is Yang Jiao? Yang angle-the external angle of all included angles of the building is Yang angle. For example, the four corners of an independent rectangular column, the corner of the outer wall (but not the corner between two walls) are all positive angles.