A substantial number of people are familiar with the phrase continuity test: does current flows from point A to point B? A hipot test is the exact opposite of a continuity test.
Hipot is short for High Potential, i.e. high voltage. In simple terms, a hipot test is normally used to check whether there is good isolation or not and is generally used to ensure that there is no current whatsoever flowing between two points.
This test is done in a simple manner involving the use of two isolated conductors. Very high voltage is then passed through them. A technician uses testing instruments that measures the current flowing between the two points.
There is a simple illustration on the Cirris System website depicting high voltage cable testing. They say a picture is worth a thousand words and that clip is definitely worth a visit.