1. The distance to which it is possible to see under prevailing atmospheric or weather conditions.
2. The relative ability to be seen under given conditions of distance, light, atmosphere, etc.: "The visibility was low because of the fog."
3. The extent to which it is possible to anticipate a future trend or situation; the "distance" that it is possible to "see" into the future.
4. The quality, fact, or degree of being visible which is perceptible with the eyes or obvious with the eyes.
5. As a measure of weather conditions, the greatest distance in a given direction at which a standard object can be seen and identified with the unaided eyes.
6. Etymology: "the condition of being seen", from Late Latin visibilitas; from Latin visibilis, "that which may be seen"; from visus, past participle of videre, "to see".

The maximum distance at which an observer can see and identify an object which is lying close to the horizontal plane on which the person is standing.

The ratio of the minimum signal input-signal power which is detectable by ideal instruments connected to the output of a receiver, to the minimum signal power detectable by a human operator through a display connected to the same receiver.

1. A type of photometer that operates on the principle of artificially reducing the visibility of objects to threshold values (borderline of seeing and not seeing) and measuring the amount of the reduction on a standard scale.
2. An instrument; such as, a transmissometer (device used to measure the transmission of light through a medium), for making direct measurements of a visual range in the atmosphere or of the physical characteristics of the atmosphere which determine the visual range.
3. A photometric device for determining the range of visibility during daylight hours.

The measurement is made visually and the visibility meter is also used in lighting engineering for measuring the values of light (brightness) contrasts between an object and the background against which it is found or projected.

At meteorological stations visibility meters are used to measure the transparency of the atmosphere in a horizontal direction by measuring the contrast of a remote dark object; for example, a forest, against the background of the sky. There will be less contrast as the air transparency decreases.