'Incidence' definitions:

Definition of 'incidence'

(from WordNet)
noun
The relative frequency of occurrence of something [syn: incidence, relative incidence]
noun
The striking of a light beam on a surface; "he measured the angle of incidence of the reflected light"

Definition of 'Incidence'

From: GCIDE
  • Incidence \In"ci*dence\, n. [Cf. F. incidence.] [1913 Webster]
  • 1. A falling on or upon; an incident; an event; an occurrence. [Obs.] --Bp. Hall. [1913 Webster]
  • 2. (Physics) The direction in which a body, or a ray of light or heat, falls on any surface. [1913 Webster]
  • In equal incidences there is a considerable inequality of refractions. --Sir I. Newton. [1913 Webster]
  • 3. The rate or ratio at which something occurs; as, the incidence of murder in Los Angeles; the incidence of cancer in men over 50. [PJC]
  • Angle of incidence, the angle which a ray of light, or the line of incidence of a body, falling on any surface, makes with a perpendicular to that surface; also formerly, the complement of this angle.
  • Line of incidence, the line in the direction of which a surface is struck by a body, ray of light, and the like. [1913 Webster]