Hyperbolic Functions
There is a physical interpretation
(from http://en.wikipedia.org/wiki/Hyperbolic_functions)
Just as the points (cos t, sin t) define a circle, the points (cosh t, sinh t) define the right half of the equilateral hyperbola x?- y?= 1. This is based on the easily verified identity ......
Read freely - they are also used in coordinate transforms in SAR imagery