I've been looking about on #MSWL on Twitter, and I see editors using some kind of informal scale for the intensity of the sexual content in a romance novel. For example: "sweet to hot," "erotic," "hot to erotic," and so-on. What does this mean? What can I expect from a sweet novel as opposed to a hot novel? Is this common jargon? What are the origins of this scale? Does it only include sweet, hot, and erotic?
I'm not well versed in romance novels, but I did run across this stuff while I was researching for a game I was writing. So while I can't tell you anything about origins, I can tell you some pretty basic stuff about the heat/sensuality system. That's what this is called, in case you want to look it up.
First and foremost, this system is not standardized... at all. Some people use different words that may or may not be clear, some have way, way more stages than others-- If I were you, I'd ask people for scales if you're getting stories (or giving stories) to them. Personally, I'd be surprised if the people who are asking for manuscripts on Twitter using that hashtag have a system in play for romance novels in particular. I mean, maybe they do? But I think most people use the three most basic levels for the systems I've come across.
Generally speaking though, I noted that most systems had a system similar to this in play:
Kissing Only: In which there is nothing but kissing in the story. This one is usually combined with the next one, but some people do explicitly mention that there's no sex/sensuality/physical romance and there's only kisses. There isn't even any allusions to anything other than kissing. This is extremely heavy on emotional aspects of the characters. I figured it would be worth adding in because occasionally people ask for "kissing only" stories.
Sweet/Subtle: While the naming convention varies, this basically is either nothing but kissing or kissing and touching. But generally, no descriptions of physical romance. If it happens, the focus is on the emotional aspect of it and it's almost always an allusion. From what I understand, there's no use of euphemisms either.... I guess that varies depending on author, though?
Warm/Hot: Basically moderate to explicit sensuality. Physical things are described, but not graphic on the warm end of this stage, with a lot left to the imagination. And euphemisms, lots of those. But there's still a focus on emotions and feelings, and there aren't many scenes when people are doing anything physical, like... one or two at best. On the hot side, explicit scenes are explored to a much more graphic end. There are more physical scenes, the scenes are longer, and euphemisms again are heavily used. But emotions and feelings are still pretty important. I've sometimes heard this just called "romance" while the stage above is called "sweet" or "love" and the stage below is called "romantica", but I'm not sure if that's mainstream.
Romantica/Erotica: This is the thin line between romance and erotica. Although it has a tendency to just be erotica (in which there is a heavy focus on physical aspects with very little emotional focus). In these there's almost no euphemisms and the focus is on physical things, so the focus on emotions and feelings dies down a bit. In return, there's a large focus on desires/sexual feelings. And sometimes these books can literally just be about sex. These are as graphic as you can get, too. Romantica is the "low" end here. It has some emotional aspects, but it's played down a lot. It uses euphemisms, though not necessarily sparingly. Meanwhile, erotica is just on the cusp of not being romance anymore. It loses most of the euphemisms and feelings. It's pretty much as close as you can get to just writing a sex book without writing a sex book.
Erotic: Sex. The book. It's literally just people having sex. And for the most part, it's really, really detailed, includes fetishistic things, has a tendency to focus on desires, and doesn't at all dwell on emotional things. And euphemisms go out the window. This is usually not even considered as a stage because erotic stories and romance stories are profoundly different. When people do consider it, they're usually combining it with the stage above.
This list is based on stuff I picked up in a forum and this was some time ago... so this scale is sort of iffy at best. But the sensuality scale is something publishing companies (that specialize in romance) apparently do a lot. Here's an example of one for Turquoise Morning Press, although I've... never heard of them. I think Harlequin Romance is the most popular published of romance novels, and I'm pretty sure their ranking system is their series names? I remember that they have series called "Heartwarming" and "Blaze" and I think that's their ranking system.
In any case, different companies/people rate stories in different ways, but the scales are similar enough that this might work for you.