Intensity \In*ten"si*ty\, n. [LL. intensitas: cf. F. intensit['e]. See Intense.]

1. The state or quality of being intense; intenseness; extreme degree; as, intensity of heat, cold, mental application, passion, etc.

If you would deepen the intensity of light, you must be content to bring into deeper blackness and more distinct and definite outline the shade that accompanies it. --F. W. Robertson.

2. (Physics) The amount or degree of energy with which a force operates or a cause acts; effectiveness, as estimated by results produced.

3. (Mech.) The magnitude of a distributed force, as pressure, stress, weight, etc., per unit of surface, or of volume, as the case may be; as, the measure of the intensity of a total stress of forty pounds which is distributed uniformly over a surface of four square inches area is ten pounds per square inch.

4. (Photog.) The degree or depth of shade in a picture.

Source: Webster's Revised Unabridged Dictionary (1913)