Hmm, I wrote somewhat similar definition in forum #210782

sex is a specific form of sexual activity that involves two or more characters where one character is directly or indirectly interacting with genitals of the other character in a pleasing way.

Comparing to Clawdragons:

if there are two or more characters, and they are engaging in some sort of physical contact (or physical contact by proxy - such as a sex toy) which is able to, at least theoretically, result in an orgasm for at least one of them

The two differences are, he mentions orgasm, but I mention genitals. I would argue that orgasm isn't necessary for sex. The other difference is, that I mention "sexual activity", which is more broad than sex.