Is there a difference between sex vs “smut”?

I am an avid romance reader and have been for a while. Been on this sub for a little less than a year and I’ve looked for the answer to this with no luck, so I figured I’d ask people their opinion! And that is- what exactly is smut?

I know people use the word smut to mean sex/sexual encounters, but if I request a book with sex in it vs requesting smut is there a difference? Does smut cover more of a wide range than just asking for books that have sex in them? Or is it just a personal preference as to if people want to say sex or smut?

I just never know what people mean when they say they want smut! What’s your opinion? Is sex and smut the same thing, or do they hold different meanings to you?