Question: In an aircraft with a reciprocating engine, the engine will be lubricated by either a dry- or wet-sump oil system. What is the difference?
Answer: The basic difference is in where the oil is stored. In a wet-sump oil system, all of the oil is contained in the sump, which is an integral part of the engine. In a dry-sump system, oil is stored in a separate tank and pumps are used to circulate it through the engine. (Source: Pilot's Handbook of Aeronautical Knowledge, page 6-15)