A quadrilateral given by its four corners, such as a glyph's box mapped from text space into page space: a rectangle in its own space, which a rotation, skew or reflection turns into a general parallelogram.
public Quad(PathPoint BottomLeft, PathPoint BottomRight, PathPoint TopRight, PathPoint TopLeft)
The corner at the box's origin side, on its bottom edge.
The corner at the box's far side, on its bottom edge.
The corner at the box's far side, on its top edge.
The corner at the box's origin side, on its top edge.
ISO 32000-2 §8.3.2 (coordinate spaces) and §9.4.4 (the text rendering matrix). The corners are named for the box they come from (bottom on the baseline side, left at the origin side), not for where they land: in text rotated by 180 degrees the BottomLeft corner is at the top right of the page.