I’ve now read dozens of definitions and discussions of romance and of erotica and of erotic romance, and after all my reading, I’ve come to the following conclusions, none of which have anything to do with the quality of the writing or the style of the writing or who is reading it and for what purpose.
Erotic romance, in my mind, is just romance. I don’t care how much sex is in it, or how that sex is portrayed. When I read “erotic romance” I read it as if it’s romance, with those genre expectations in mind: happy ending and focus on the growth of a couple’s romantic relationship (and sometimes a threesome’s romantic relationship).
Erotica, to me, includes plotless or “stroke” fiction which is sometimes termed pornography as well as literary erotica. Mainly, though, I think of erotica as any work in which sex is a major component. The story doesn’t have to focus on the development of a couple’s relationship; it might focus on a couple, or it might focus on several groupings of different types. The story does not have to have a happy ending. It may include couples and happy endings, but it doesn’t have to.
I think of erotic romance as a subset of erotica, not the other way around. To me, erotica is an inclusive term for the literature of sexuality.
Your mileage, of course, may vary considerably.
Related post: Erotic Journeys and Bodice Rippers.