You can date how long someone has been in the door and hardware industry by how they explain how to hand a door. 

People in the industry for 30 years or more have heard the term “put your butt to the butts” in order to hand a door. At one time hinges were called butts.

The Door and Hardware Institute (DHI) has this tip. “Make sure you are on the correct side of the door which is the secure side or key side. This is determined with “to” and “from”.  “To” indicates a door swing into a building, room or space.  “From” indicates a door swing out of a building, room or space.” 

Having a cheat chart is the easiest way if you are new to the industry. This is the most straightforward chart we have found for single and pairs of doors.