Unimatrix shielding was an advanced form of protective energy screen technology, invented by Lieutenant Commander Tuvok for use on the USS Voyager's multi-spatial probe in 2375. Later, Tom Paris applied Tuvok's shield designs for the Delta Flyer. (VOY: "Extreme Risk")
According to Star Trek Encyclopedia, unimatrix shielding technology was employed in the immersion shielding deflector technique.