noun

• The act of something happening; occurrence.
• The extent or the relative frequency of something happening.
• The manner of falling; bearing or onus, as of a tax that falls unequally.
• (physics) The striking of radiation or a projectile upon a surface.
• (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.