In fan fiction and erotic fiction, dubcon (also dub-con and occasionally dub!con) is a keyword or hashtag indicating that the story contains one or more sexual encounters where one or more parties gave only "dubious consent." This is seemingly in contrast to other keywords such as "consensual," "noncon" (ie "non-consensual"), and flat-out "rape."
To me, this is an absurd term marking a distinction without a difference. The term seems to be most commonly attached to stories where someone is initially curious but then gets raped, or where someone initially says no, gets raped, and then later decides they liked it. So in other words, when you see "dubcon" attached to a story, someone is going to get raped. So they should just call it what it is, instead of trying to make it seem somehow less bad.
As society moves from an older definition of rape, based on "No means no," to a more complete definition where "Only yes means yes," we need to adjust our understanding of what really qualifies as "consent" in a sexual encounter. Yes, even in fan fiction. Because anything other than robust consent is not consent, and "dubious" consent is not consent at all.