How do you classify movies like - The Shining, Saw, Psycho, Halloween, Psycho, Silence of the Lamb, Carrie, Scream, Body Snatchers, Get Out, Rosemary's baby etc.

Hitchcock did plenty of thrillers that weren't horror. They are films that run on tension. Horror runs on dread, despair, gore, shock. You can have horrorfic iconography or scenes of despair that are not in themselves tense or suspenseful. Think, Frankenstein carrying the girl's body into town.

Of course, there is a lot of overlap. Halloween is an extremely tense movie as Michael Myers skulks the shadows. He never even runs. It's very disquieting. The camera also takes his POV and tracks his victims. It's pretty thrilling. There is always suspense before a kill.

The amount of gore or supernatural s*** mostly distincts a horror film from a thriller imo

so if you had to classify it in 1 category which is it?

Genre is just a construction. "Horror thriller" and "crime thriller" are more helpful in distinguishing them.

Most horrors have thriller elements, but not all thrillers have horror elements.

every movie has 1 major genre

not true

give me an example of a movie that is not 1 genre

You're the expert. You decide!

Thrillers present tension in practical ways, usually, scenarios, amplified by their proximity to real life imo

Where as horror does needs some sort of overt “display” rosemary’s baby is a thriller to me right up until that infamous scene, old boy is a horror movie to me as well honestly for similar reasons..

I really don’t consider something like Silence of the Lambs any sort of horror movie though it’s a crime thriller with overwhelming atmosphere, nothing that exist in that film couldn't take place in real life

Parasite
Three billboards
Uncut gems

I don’t think any movie is strictly one genre. Even romance flicks falls under Rom/Drama or Rom/Comedy

Thrillers can be non-horror flicks such as Uncut Gems and Collateral. It’s about the tension.

Uncut Gems - Thriller

Horror is about an attack on innocence within vulnerability. It’s why signature horror traits include: being haunted in a nice house, being attacked in a shower or during sex, attacking young women etc

It’s also about the grotesque

Horror is scary
Thriller is thrilling

Thriller >>>>>>> Horror

It’s also crime and dark comedy

what about serial killer movies and italian giallo horror without supernatural elements?

Ok, human 13 with the great summary

serial killer movies really depend. Something like Texas chainsaw massacre is obviously more gory than something like The Zodiac where the murders themselves aren't really the main focus of the story. Italian Giallo are often very bloody from what I've seen, but I guess some can be considered thrillers.

People in the “horror community” find these distinctions annoying. I have to agree. Thriller is a term often used to make certain action and horror films seem more respectable. The academy didn't want to give a horror film the best picture award so Silence of the Lambs was slapped with the thriller tag.

Jumpscares and supernatural stuff

Freddy vs Alien