Scream (films) Universe

The Scream (film series) universe refers to the fictional universe similar to real-life events up until 1996 and onward, with the general exception being the release of the Scream films, its characters and cultural impact. It is generally used as cultural commentary on slasher films and the film industry in general.

Original film
Due to the events of the original film not being adapted into a film yet, it technically retains all key elements of the real world (acknowledging Jamie Lee Curtis as a Scream queen, etc.). All the films still serve as meta slasher commentary, with self-aware commentary on horror films (and sometimes the film industry in general).

Second film onwards
The sequels elevate this with a fictional film series based on the events of the original film. For example, the Scream films themselves do not exist in the Scream universe, as they are "true events". Heather Graham is regarded as the iconic opening scene actress of the film, Stab, and Drew Barrymore did not portray Casey Becker (because Barrymore portrays Becker in the actual film).

There is a fourth wall breaking moment in the third film, in which Bianca Burnette (portrayed by Carrie Fisher, who complains that others say she looks like Carrie Fisher) tells Gale Weathers, "or do you want me to tell you who you look like?" (a reference to actress Courteney Cox herself).

As Cox was of Friends fame at the time and starring in it simultaneously with the original Scream trilogy, her co-stars are mentioned in the franchise, including Jennifer Aniston, whose body was used for photoshop for Gale's "leaked nude pictures" on the internet, as mentioned as an in-joke in Scream 2 (1997 film). David Schwimmer is the actor to portray Dewey Riley in the first two Stab films as well.

Fourth film
The fourth film elevates this with the idea of the Stab films themselves being meta commentaries on horror. Stab 7 appears to be set in the "real world" (the Scream universe) where actress Kristen Bell portrays one of the two Ghostface killers, Chloe. Chloe is a fan of the previous six Stab films because they're "scarier" and acts as a piece of commentary on Scream 4 (2011 film) justifying its existence against backlash and haters (Rachel, portrayed by Anna Paquin in this case) of being an unnecessary cash-grab sequel.

Given it is the seventh film and the film it is portrayed in is directed by Wes Craven, it is most likely an homage to Wes Craven's New Nightmare (1994 film), where the events of the first six Nightmare on Elm Street films were fictional and Heather Langenkamp who portrayed Nancy must return to the role one last time as Freddy enters "the real world".

Actor substitutes
On Reddit, co-directors Matt and Tyler answered a question from fans regarding Scott Foley (who portrayed Roman Bridger in Scream 3)'s appearance in Dawson's Creek, that appears as an homage in the fifth Scream film. They suggested that this is actually Roman Bridger himself, during his guest actor stint, a case where Scott Foley either does not exist in this world, or look-alike Bridger took his part, similar to Fisher taking Bianca Burnette's role as Princess Leia in Star Wars.

Parodic elements

 * Casey Becker in the Stab film is a parody of horror films' unnecessary nudity and nonsensical character actions, as she is both making popcorn and taking a shower.
 * Tori Spelling portrays Sidney Prescott in at least the first two Stab films. The original film makes a joke "With my luck, they'd cast Tori Spelling" when Sidney is asked who they think will play her if they make a movie on her life, and carries this joke onwards in the sequels. (Real-life Tori Spelling was not offended by it, and Neve Campbell who portrays Sidney sent her apologies for having to say the line).
 * Alicia Silverstone portrays Tatum Riley, a reference to Stu's response to Tatum after she says "As if" in the original film, a notable catch phrase by Silverstone's character in the 1995 cult classic high school film, Clueless.