Chirality and handedness are concepts that apply to the structure of molecules. Chirality is defined by the lack of certain features of symmetry, which lead to an object not being superimposable on its mirror image. Handedness is a different phenomenon relating to the ability to classify chiral objects into right-handed and left-handed objects. All handed objects are chiral, but not all chiral objects are handed. In 1968 through 1970, Ruch and coworkers developed a theory of chirality that provided a mathematical basis for the handedness of chiral objects. Handed chiral objects are considered to be analogous to shoes, which are readily classified into right and left shoes regardless of the size, material, style, or other attributes of the shoes in question. Nonhanded chiral objects are considered to be analogous to potatoes, which have no symmetry because of their irregular patterns of "bumps" and "eyes," thereby meeting the lack of symmetry requirements for chirality. There is, however, no unambiguous way to classify a set of potatoes into "left" and "right" potatoes. [Go to source
When viewing the door from outside*, handedness is side on which the door hinges are hung. For example, a left-handed door would have the hinges on the left side of the doorframe and open inwards. Most doors open inwards; reverse left-hand and reverse right-hand are defined as doors that swing outwards. Door handedness is important when choosing some door hardware, such as levers and mortise locks, but is most often unimportant for knobs, handles, or other hardware that can fit either left- or right-handed doors. *Outside is defined as outside the house or outside the room the doorway leads to.
This specification is necessary when purchasing a “half-dummy” lever (single surface-mounted lever). Lever handedness is determined by which direction the lever handle will point, not by which side of the door it is mounted on. For example, a left-hand lever will be mounted on the right side of the door with its handle pointing toward the door hinges on the left.
Handedness is an attribute of human beings defined by their unequal distribution of fine motor skill between the left and right hands. An individual who is more dextrous with the right hand is called right-handed, and one who is more skilled with the left is said to be left-handed. A minority of people are equally skilled with both hands, and are termed ambidextrous.