The term isocline derives from the Greek words for "same slope." For a first-order ordinary differential equation is, a curve with equation for some constant is known as an isocline. In other words, all the solutions
of the ordinary differential equation intersecting that curve have the same slope
. Isoclines can be used as a graphical
method of solving an ordinary differential
equation.

The term is also used to refer to points on maps of the world having identical magnetic inclinations.