cusp

In architecture, the point with curved sides which decorates the apertures of Gothic tracery. Three or four cusps within a circle produce clover shapes called trefoils or quatrefoils.

Cusp may refer to any of the following:

In common parlance, a cusp is an important moment usually regarded as a decision point upon which consequent events are determined. More literally, a cusp is a sharp point or apex, such as occurs in two dimensions at the end of a crescent, or in three dimensions at the tip of a cone or horn. a singular point of a curve; a conical singular point seen in hyperbolic geometry; a missing point on a modular curve that has to be supplied by compactification; In dentistry, a cusp is any of the points on a cuspid (canine tooth) or molar. If an internal link led you here, you may wish to change the link to point directly to the intended article.