Clearance is defined as the shortest distance
through air between two conductive parts. Breakdown along a Clearance path is a fast
phenomenon where damage can be caused by a
very short duration impulse. Therefore, it is the
maximum peak voltage, including transients, that
is used to determine the required Clearance
spacing according to charts given in the standard.

Creepage is defined as the shortest distance
between two conductive parts along the surface
of any insulating material common to both parts.Breakdown of the Creepage
distance is a slow phenomenon, determined by dc
or rms voltage levels rather than peak events.