Definition of "incidence"

The act of something happening; occurrence.  examples

The extent or the relative frequency of something happening.  examples

The manner of falling; bearing or onus, as of a tax that falls unequally.  examples

(physics) The striking of radiation or a projectile upon a surface.  examples

(epidemiology) A measure of the rate of new occurrence of a given medical condition in a population within a specified period of time.

(geometry) The falling of a point on a line, or a line on a plane.  examples