The Collaborative International Dictionary
Equipotential \E`qui*po*ten"tial\, a. [Equi- + potential.] (Mech. & Physics) Having the same potential.
Equipotential surface, a surface for which the potential is for all points of the surface constant. Level surfaces on the earth are equipotential.
Wiktionary
n. Any n-dimensional surface (or line) having a constant scalar potential
Wikipedia
Equipotential surfaces are surfaces of constant scalar potential. They are used to visualize an (n)-dimensional scalar potential function in (n-1) dimensional space. The gradient of the potential, denoting the direction of greatest increase, is perpendicular to the surface.
In electrostatics, the work done to move a charge from any point on the equipotential surface to any other point on the equipotential surface is zero since they are at the same potential. Furthermore, equipotential surfaces are always perpendicular to the net electric field lines passing through it.
Since all points on a sphere around a test charge are equidistant, using the formula V= KQ/r it can be concluded that the charges will have the same potential difference.
The term is used in electrostatics, fluid mechanics, and geodesy.
Usage examples of "equipotential surface".
In the language of physics, the stratus forms an equipotential surface in the gravitational field permeating the earth's atmosphere.
The geoid is the equipotential surface of the earth's gravitational field that approximates the mean sea surface.