The Pi was a Romulan scout ship that was in service with the Romulan military in the mid-24th century.
In 2366, the Pi, crewed by Patahk and Centurion Bochra, was carrying out a covert mission when it crash landed on the planet Galorndon Core, inside Federation space. The Pi was destroyed with an ultritium explosive after the crash to prevent its capture by Starfleet. Both Romulan crew members were eventually retrieved by the USS Enterprise-D. Patahk died from his injuries, while Bochra was returned to the Romulans. (TNG: "The Enemy")
The mission of the
Pi was not revealed in the episode.
The name Pi was later used for a Romulan
Griffin-class ship instead of the scout ship type in the game Star Trek: Armada.
Pi was a Greek letter
, although it was unknown if there was any relation. In this usage, though, the "relationship" is most likely simply homophonic.