Terms of orientation, terms of location, or spatial words are common linguistic descriptors used to indicate the spatial positioning of objects in three-dimensional space, including notions of top, bottom, front, back, left side, and right side as used in everyday language and interactions.
Linguist Eve V. Clark notes that "many objects in the world around us have an inherent orientation that we usually take for granted".
For example, "a candle has an intrinsic top and bottom, because its canonical position is upright with certain defining features at each end.
For some uses, where it is necessary to avoid confusion from differences in viewpoint, separate terminology is used to describe the sides of things.
[8] Similarly, port and starboard are nautical terms for watercraft, aircraft and spacecraft, referring respectively to the left and right sides of the vessel, when aboard and facing the bow (front).
[9] The existence of anatomical terms of location is a reflection of the tendency of living things, more than naturally occurring nonliving objects, to have an orientation, described by the concept of body relative direction.
Aristotle reasoned that concepts of "front" and "back" were only relevant to animals with the ability to perceive these relative positions.
[12] It is further observed that an animal lacking a distinct front and back has "a disadvantage in directed locomotion", meaning that this form is "most typical of free-floating organisms that do not move under their own power".
[12] A ping pong ball, like the orange one pictured below, is a uniform sphere, and is therefore a typical example of an object that has no set top, bottom, front, back, or sides;[13] it only has these characteristics in a contingent and temporary sense relative to the viewer.
The ball, seen from above in the picture, could be described as having its "top" facing the viewer and its "bottom" obscured, or could be described as having its "top" and "bottom" as the uppermost and lowermost points visible to the viewer relative to the screen on which the object is being viewed.