From the time when I first began reading this type of fiction (in the form of 'streaking' stories), and later also seeking out pictures and videos with the same themes, I have gotten to learn that there are a lot of acronyms used to describe what the scenario you are reading about or watching contains. While they might be impenetrable to people who don't know this particular field/kink, they are very useful to those that do.
I recently contributed to a discussion on the Literotica forum about such acronyms and I thought I would expand here on some of the examples I gave and what, to me, I expect to find when reading a story with those tags.
CFNM (Clothed Female/Nude Male)
Probably the most fetish-y of the tags, this usually denotes a scenario in which a man is nude in front of a woman, and he is a submissive while she dominates and/or humiliates him. She might mock his nudity or penis size, force him to perform the duties of a slave, exhibit him for other women, force him to masturbate in front of her or others, or masturbate him herself (usually not in a loving way!). Of course, like all good BDSM the man is a willing participant in this, usually (as is the case with most non-consensual stories) being initially persuaded against his will before discovering that he likes it.
Less commonly, it can also mean a male exhibitionist exposing himself to a woman in a less power-dynamic based way (for example, a man agrees to model nude for a female artist friend, and through this sexy times ensue).
CMNF (Clothed Male/Nude Female)
This can also be BDSM-based; a female slave/pet who is naked for her clothed master is not uncommon. Most people who write these type of scenarios have read at least one John Norman Gor book! Usually an element of humiliation is involved but sometimes the nude/clothed balance is used just to denote who is subservient to who; lack of clothing 'lessens' the parts of the submissive's identity that are independent of the master.
However CMNF can also be more broadly applied, to scenarios where a woman is naked in the company of a clothed man for mutual pleasure or her own pleasure. Stories where a man has a female partner who is an exhibitionist fit this category.
CMNM (Clothed Male/Nude Male)
Basically the gay version of CFNM. Submissive male is naked as part of being dominated by one or more other men. Usually the clothed male is dressed in a way that denotes extra power (suits and uniforms are common).
Less common, this can form the basis of gay first time/experimentation stories, although usually these quickly become NMNM!
CFNF (Clothed Female/Nude Female)
Can be lesbian dom/sub scenarios, even in a broad sense (strict college professor forces female student to strip for punishment, for example), but not exclusively. Sometimes in CFNF scenarios the "dominant" character is the one naked, with their nudity denoting sexual confidence rather than submission/humiliation.
Best Friends With a Naked Girl is a CFNF story in which, for the most part, the nude female (Becky) calls the shots, and the clothed female (Lisa) allows Becky to assert her wants onto her. Becky is constantly portrayed as the more confident of the two, and the one more in touch with her own sexuality.
ENF (Embarrassed Nude Female)
The classic 'caught naked' scenario. Character finds themselves naked in front of other people when they don't want to be, and end up red-faced by being exposed. Of these categories this is the one most used in mainstream fiction/cinema (think Daryl Hannah locked out of her house naked at the start of the movie Roxanne, or the "character X walks on on character Y in the shower" trope in many sitcoms). In erotica, the character usually ends up aroused/excited by the experience (again, as is common in scenarios which begin in non-consensual experiences).
While ENF could begin with a character losing their clothes and instantly plunged from comfort to humiliation, another popular scenario is for a character to begin with consensual nudity (e.g. skinnydipping or nudism) which later progresses to them being seen naked in a way they did not want to be.
CNF (Confident Nude Female)
A less common term, but basically the opposite of ENF. Here, the woman is naked in front of others because she wants to be, and she knows exactly what she is doing. Often the excitement in the story comes from the juxtaposition between her confidence in her body and sexuality, and the reactions it causes in others. Usually, these are stories about female exhibitionists, although "this is me in my natural state, deal with it" nudist characters are also common.
My favourite type of character to write. Becky in Best Friends is your textbook CNF - she has no embarrassment about being seen naked, even if it causes embarrassment in others.
Can show up in mainstream stories; think Alexis Dziena walking around naked in front of a surprised Bill Murray in Broken Flowers.
OON (Only One Naked)
A progression from CxNx stories where the character is naked around and in front of a whole bunch of people. Their nudity is more greatly emphasised because they are outnumbered by people who aren't naked. Can be humiliating (being seen naked by many people is worse than being seen naked by one) or exciting for them (if being seen naked by one person feels good, then the more the merrier!).
Nude in School/College type stories like DH Jonathan's The 'Volunteer' use the OON scenario (nobody else is walking around naked except Dani, and she is frequently in the company of a great many clothed people); in this instance, being the only naked person "others" the character and marks them as different as usually in these situations nudity is not socially acceptable.
Stories of nude life-modelling for art classes are also in this realm.
NIP (Nude In Public)
Fairly self explanatory. Character is naked in a public place where nudity would not be the norm. I tend to restrict this tag to stories where characters are nude in places where it is almost certain that other members of the public will see them (for example, the street, a college campus, a shopping mall, a subway station, a movie theatre, a public park...) - a hike nude in quiet woodland might technically be public, but the expectation of the reader of an NIP story is usually for greater exposure than this.
Character who is nude might be an ENF or a CNF, or start as one and end up as the other!
F2S (Forced to Streak)
I don't see this much any more, although it used to be more common as there was a web forum dedicated to such stories. In them, a character is naked, usually in an innocent way (skinnydipping or being accidentally locked out of a house naked are common) and then discovers their clothing is missing, or destroyed. They are therefore left with no choice but to run naked from a place in which their nudity is concealed, through a more public setting, until they reach safety (either home or their car, or some means of clothing themselves).
Of course, as with the other stories in which the character is naked against their will, they might well find as the story progresses that they actually find the risk and/or humiliation exciting.
F2S could also be confused/interpreted as Forced to Strip, which I suppose might be one reason it isn't used much (although such stories, in which a character is undressed, or made to undress, against their will, tend to be tagged as Forced Stripping in my experience).
I'm sure these aren't the only acronyms in our world of erotica, and I'd love to hear new ones I've not encountered before, or your take on what you expect when you see those above.