Implicit Function

A function which is not defined explicitly, but rather is defined in terms of an algebraic relationship (which can not, in general, be ``solved'' for the function in question). For example, the Eccentric Anomaly $E$ of a body orbiting on an Ellipse with Eccentricity $e$ is defined implicitly in terms of the mean anomaly $M$ by Kepler's Equation

$$M = E-e\sin E.$$