Pr is the hieroglyph for 'house', the floor-plan of a walled building with an open doorway. Though its original pronunciation is unknown, modern egyptology assigns it the value of Per.
Pr combined with an associated "personal name", god, or location becomes the "House of .... ." An example for pharaohSetnakhte is the city of: Pr-Atum, (city of Pithom).
The shape of Pr in beginning dynasties had variations in the shape of a square, with the opening. See Garrett Reference for tomb of Official Ti.
Pr and Ankh-(Life) is a "combination hieroglyph" and is the "word" for House of Life. The House of Life is a library for papyrus books-(scrolls), as well as a possible scriptorium.