Matthew was a genetically-engineered Human child who lived in the Genome colony on Moab IV during the 2360s.
Matthew performed Chopin's Prelude Number 4 on the piano during an outdoor concert for the Genome colonists and the visiting crew of the USS Enterprise-D in mid-2368.
During the concert, Matthew was briefly interrupted by an earthquake, but was encouraged to play on by the colony's leader, Aaron Conor. (TNG: "The Masterpiece Society")
Matthew was played by featured actor Daniel Fawcett.
While named in dialogue, he was simply described in the script
as a "12-year
". The call sheet is listing him as "musician".