What is "submarine patent"

n. (context informal English) A patent first published and granted long after the filing of the initial application.

A submarine patent is a patent whose issuance and publication are intentionally delayed by the applicant for a long time, such as several years. This strategy requires a patent system where, first, patent applications are not published, and, second, patent term is measured from grant date, not from priority/filing date. In the United States, patent applications filed before November 2000 were not published and remained secret until they were granted. Analogous to a submarine, therefore, submarine patents could stay "under water" for long periods until they "emerged" and surprised the relevant market. Persons or companies making use of submarine patents are sometimes referred to as patent pirates.

The phrase is occasionally used more generally for any patent used in patent ambush.