“Giallo” is mainly an Italian subgenre of thriller film. Giallo films are known for their unusual musical arrangements, convoluted whodunit plots, excessive bloodletting, sexual imagery and operatic visual style. They were made popular in the late 60’s and early 70’s by directors such as Mario Bava, Dario Argento, Sergio Martino, Lucio Fulci and Umberto Lenzi.
Here are the best giallo films available here on Mubi, according to yours truly at least. Several key entries to the genre are missing, so the list is far from complete. Still this should give you an insight to the giallo genre.