Leakage current is generally a current that flows in an insulating material (insulator).
Any currents that flow through the insulator during the withstanding voltage and insulation resistance tests or leakage current test are all referred to as a leakage current.

However, for example, in the international standard IEC60990:1999-08 (methods of measurement of touch current and protective conductor current), the term of ‘leakage current’ is not used, and the terms of ‘touch current’ and ‘protective conductor current’ are used instead.
In any of these tests, the insulator is considered to have poor performance if a leakage current flows.
The higher leakage current can cause an electric shock or fire hazard.