Threshold

A threshold is typically a minimum value for a quantity; or in a building, a strip of wood, metal or stone located on the floor in a doorway following the line of division between the two spaces linked by the doorway.

• In telecommunication, the term threshold has the following meanings:
  1. The minimum value of a signal that can be detected by the system or sensor under consideration.
  2. A value used to denote predetermined levels, such as those pertaining to volume of message storage, i.e., in-transit storage or queue storage, used in a message switching center.
  3. The minimum value of the parameter used to activate a device.
  4. The minimum value a stimulus may have to create a desired effect.
  • Source: from Federal Standard 1037C and from MIL-STD-188

• In electrical engineering and machine learning, a threshold circuit or unit is a one-input, one-output device or object that implements a Heaviside step function.

A literal meaning of the term threshold, is "that which holds thresh", and the word derives from the practise, in antiquity, in certain types of dwelling in England, to lay straw (or "thresh") down on an earth floor to provide a relatively warm and clean floor. The threshold was a strip of wood at the doorway which prevented thresh from migrating through the doorway as it was used by the occupants of the dwelling.