What is an isocline?

http://en.wikipedia.org/wiki/Isocline An Isocline is a series of lines with the same slope. The Word comes from the Greek Words Isos (Ίδιος) meaning "same" and Klini (κλίση) meaning "slope." It is often used as a graphical method of solving ordinary differential equations. In an equation of the form y' = f(x), the isoclines are given putting f(x) equal to a constant. This gives a series of lines (for different constants) along which the solution curves have the same gradient. By calculating this gradient for each isocline, the slope field can be visualised; making it relatively easy to sketch approximate solution curves; as in fig. 1. In population dynamics refers to the set of population sizes at which the rate of change, or partial derivative, for one population in a pair of interacting populations is zero.