No, I am most definitely not speaking of the Argento film that goes by the title of Giallo. Let's talk about the origin of the word and what it encompasses, yes?
Giallo is an Italian 20th century genre of literature and film. The word "giallo" is Italian for yellow and refers to a series of cheap paperback mystery novels that have trademark yellow book covers. So, naturally, giallo is a direct inference that you are about to immerse yourself in crime fiction and mystery.
Originally, the crime/mystery pulp novels, titled Giallo Mondadori, were published in 1929 by Mondadori and they all had that recognizable yellow cover. The series was mostly Italian translations of mystery novels from British and American writers. Published as cheap paperbacks, as their popularity grew other publishing houses began to follow suit and mimic the yellow cover. Eventually, the word giallo was established as a shortcut word for a pulpy mystery novel.
When it comes to cinema, the term giallo has come to refer to any kind of thriller; regardless of origin, any thriller may be deemed giallo. Alfred Hitchcock's Psycho and Vertigo are prime examples of giallo, as is the classic horror film Pepping Tom. For English speaking audiences, specifically, giallo has come to be more of a specific term, often naming Italian produced thrillers or "spaghetti thrillers" as giallo films. As the genre matured, it began to define a unique kind of horror/psychological thriller which would later prove to be a huge influence on the emerging slasher film.
Generally characterized as gruesome murder mystery thrillers with suspense and Hitchcock-like qualities, giallo films may also feature excessive bloodletting, artful camerawork and what some would consider jarring music. (Is this sounding familiar Argento fans?) One of the most recognizable characteristics of this film genre is the music. Argento does seem to be the best representation of this with Opera and Suspiria being fantastically beautiful examples.
Mario Bava's The Girl Who Knew Too Much is considered to be the first giallo film; an obvious nod to Hitchcock's The Man Who Knew Too Much, Bava also gifted us with Blood and Black Lace. It is this film that really set the standard of the giallo recurring theme; a masked stalker, a shiny weapon and brutal murders of beautiful women. This standard plot is used in countless films and the kills are always gory. Throat slashing is a big favorite of the genre and the killings, more often than not, take place when the gorgeous woman is vulnerable (i.e.) taking a shower or otherwise barely clothed. Giallo films may also, but not as a rule, involve supernatural forces and most of them contain liberal amounts of sex and nudity. The genre also likes to feature themes of psychological madness, alienation and paranoia. Typically, a giallo film will end up revealing the killer to be mentally disturbed. For me, Dario Argento's Tenebrae is a really wonderful and prime example of a giallo type film.
Giallo had it's heyday from 1968 -1978 with 1971-1973 being particularly bountiful. Sixty five gialli films were produced in this two year time period and came from the directors, Mario Bava, Dario Argento, Lucio Fulci, Sergio Martino, Paolo Cavara and Umberto Lenzi. Not to be confused with the polisiottechi (tough cop) genre, directors and stars would often move between the two film types.
Please enjoy one of my personal favorite examples of the Giallo film genre.