Terms are below, as well as keys & legends.
Here’s my version of the basic key. And listen, I read a lot on Ao3, so my version may be a bit spicier than yours.
🌶️ = Minimal spice, maybe one orgasm, small scenes.
🌶️🌶️ = Somewhat spicy, maybe one sex scene.
🌶️🌶️🌶️ = Multiple sex scenes, they may be normal or have slight dynamics to them. This could also include non-sexual BDSM settings such as a dom/sub relationship.
🌶️🌶️🌶️🌶️ = The sex scenes may be numerous, have multiple partners, or include heavier dynamics.
🌶️🌶️🌶️🌶️🌶️ = Probably either an orgy or a monster, tbh.