A shield technology devised by the Ferengi scientist Dr Reyga that allows a vessel to survive inside the corona of a star, tested aboard an Enterprise-D shuttle in 2369.
Metaphasic shielding surrounds a ship with a field that withstands the heat and radiation of a stellar corona. It was invented by Dr Reyga, a Ferengi scientist whose work was ignored by his peers until Beverly Crusher invited him to demonstrate it aboard the Enterprise-D.
In the Next Generation episode Suspicions, the Takaran scientist Jo'Bril apparently dies during the first test flight and Reyga is found dead soon afterwards. Crusher, risking her career, flies the shuttle Justman into the star herself and proves that the shield works; Jo'Bril had faked his death to steal the invention.
The technology saves the ship in Descent, Part II, when Crusher, in command of the Enterprise, hides in a star's corona from a Borg vessel and destroys it by triggering a solar eruption.