Normal (mathematics)

The term normal in mathematics is used in the following broad senses:


 * To denote something upright or perpendicular
 * To denote something that is as it should be. In this sense, normal means good or desirable rather than typical

It is typically used as a limiting adjective, and in a binary sense. In other words, an object in a certain class is normal if it satisfies certain conditions, and every object in that class is either normal or not normal. The noun form is normality. Thus, normality can be viewed as a property in various contexts.

In differential geometry
Normal to a curve in the plane: The line perpendicular to the tangent to the curve at a point.