Virgo is a gravitational wave detector consisting of a large laser Michelson interferometer in Italy. It aims at the 10-10000 hertz frequency range, presumed to detect supernovae or coalescence of binary systems in the Milky Way and other Local Group galaxies. It is part of the European Gravitational Observatory.
It consists of laser beams enclosed in 3km vacuum chambers reflected multiple times to produce 100km paths, designed to detect minute changes in distances due to gravitational waves.
Following an upgrade completed in 2017 (aka Advanced Virgo), the detector was operated at the same time as LIGO resulting (as intended) in two detections seen by Virgo and both LIGO detectors: GW170814 and GW170817. In the latter, Virgo detected "something" but the detection wasn't clear. Given that these detectors' sensitivity depends upon the direction of the source of the signal, this fact helped localize the source and contributed to its discovery in visible light.