A piping arrangement in which a drain from a fixture, appliance or device discharges indirectly into another fixture, receptacle or interceptor at a point below the flood level rim and above the trap seal.
(International Plumbing Code® 202.0)
Plumbing Code…
A physical separation which may be a low inlet into the indirect waste receptor from the fixture, appliance, or device indirectly connected.
(Uniform Plumbing Code® 203.0)