The handing of the door refers to which way it swings. While for an exterior door you need to know if it’s inswing or outswing, for an interior door you only need to know if it is a left hand or right hand.
To determine the handing of the door, imagine the door is open and you are standing with your back to the hinges.
If the open door is on your left, it is a left hand door.
If the open door is on your right, it is a right hand door.