incidence

n. frequency, rate of occurrence; occurrence, instance; falling of a ray of light (or anything else which moves in a straight line) on a surface (Optics, Physics)

Incidence may refer to:In optics, the angle of incidence.Incidence algebras are associative algebras used in combinatorics, a branch of mathematics. See also incidence structure.Some axioms of synthetic geometry deal with a relation called incidence; see incidence (geometry).In epidemiology, there is another concept called incidence; see incidence (epidemiology).
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Noun
1. the relative frequency of occurrence of something
(synonym) relative incidence
(hypernym) frequency, relative frequency
(hyponym) morbidity
2. the striking of a light beam on a surface; "he measured the angle of incidence of the reflected light"
(hypernym) optical phenomenon

n. incidence, impact, effect

(n.)
The direction in which a body, or a ray of light or heat, falls on any surface.
  

(n.)
A falling on or upon; an incident; an event.