A post by a fellow writer here, has me mildly annoyed. The poster was ostensibly writing about what he thought of as "gay fiction."
Except it wasn't gay fiction, or even queer fiction, that is, fiction featuring same-sex attracted characters (whether gay males or lesbians or bisexual). The post was about fiction written by straight-identifying women for other straight-identifying women. It was M/M erotic fiction.
M/M erotic fiction is descended from slash—fan fiction written by (usually female) fans of a particular television show, or movie. Fan fic is not, generally, authorized by those who have creative control, and it thus presents certain cultural, ethical and legal issues. Fan fiction (fan fic), and especially slash or m/m fan fic, is mostly closely associated in terms of origins with the orignal Star Trek, and women who thought there was an unspoken, unacknowledged relationship between Kirk and Spock. You can read a Newsweek article about the phenomenon here; k/s fic was also primarily by and for heterosexual women. If you're curious about the early history of fan fic, and slash fic M/M, the first effort at serious discussion was in Star Trek Lives! By Jacqueline Lichtenberg, Sondra Marshak, and Joan Winston. Bantam. 1975. Several other attempts have been made, like 1997's Nasa/Trek: Popular Science and Sex in America by Constance Penley (Verso, 1997).
Slash fic, and fan fic in general, has blossomed since the 1970s and early K/S or Kirk/Spock erotica to be a much wider genre-crossing pairing of m/m. While m/m erotica is blatantly erotic and includes detailed erotic encounters between the protagonists, it is primarily written for, and by, straight-identifying women, with a sprinkling of women who identify as bi or lesbian. (For another perspective, see this Gayscape piece).
Driven in part by the popularity of slash m/m fic in other fandoms, like Harry Potter, but mostly, the increase in small niche erotica publishers made possible by rapid POD (digital Print on Demand) and ebooks, there are now erotica publishers who cater to M/M fiction fans. I see absolutely nothing wrong with writers and readers writing and reading fiction that targets their particular sexual fetish, turn-on, or kink, but please, let's not identify it as gay fiction. In fairness, I should note that there are a number of writers and readers who do object to M/M erotica as not just fetishizing gay sex but as appropriating queer culture.