Some definitions

Suppose f   is a complex function, and z   is a complex number.

Consider the sequence of complex numbers z, f(z), f(f(z)), ...

The sequence is called the orbit   of z   under f.

Whenever the magnitude of every complex number in the orbit of z   under f   is bounded by some constant M, the orbit of z   under f   is said to be bounded.

Otherwise, the orbit of z   under   f   is said to escape to infinity.

The Filled Julia Set,K, for a complex function   f   is the set of all points on the complex plane whose orbits under   f   are bounded.

The Julia Set,J, is the boundary of K.