A metaphasic shield was a type of shield that could be used by a starship or shuttlecraft to approach a star safely.
In 2369, Reyga, a Ferengi scientist, worked with the crew of the USS Enterprise to test a metaphasic shield. Jo'Bril killed Reyga and attempted to make steal the technology for his people, the Takarans. Jo'Bril was stopped by Beverly Crusher, who proved the technology worked. (TNG episode: "Suspicions")
Geordi LaForge later developed metaphasic shielding for the Enterprise which enabled the Enterprise to hide in the corona of a star from a Borg ship. (TNG episode: "Descent, Part II")
In 2370, the Helios managed to steal a metaphasic shield from a Ferengi trader and used it to hide in a star's corona when the Cardassians pursued them. (DS9 novel: Proud Helios)
In 2371, Chakotay ordered the shields of the USS Voyager to be modified to be metaphasic shields for Voyager to enter the corona of a G2 star. (VOY - Invasion! novel: The Final Fury)