What exactly does a 2046 house window size mean?

Depends. A 20x46 can be the glass size of each piece of glass. Odd window if it is. It can be the overall measurement of the window. It can also be a 2.0x4.6 which would be 2 ft. wide and 4 ft. 6 inches tall. Everyone needs to be sure they are using the same terms when it comes to describing Windows and doors.