You open a room and half the messages start with a code: "m4f uk, into slow build", "f4a, tell me something interesting", "t4t here". It looks like a password system and it is actually the most efficient piece of shorthand in adult chat. M4F means male seeking female, and every other tag in the family is built from the same two-part formula. Learn the grammar once and you can read an entire room in about four seconds instead of opening twenty conversations to find out who wants what.
The formula
The tag is always "who I am" + "4" + "who I want". The 4 is just the word "for". Left of it is you, right of it is the person you are hoping to talk to. That is the whole system, and every tag you will ever see is an application of it.
So m4f is a man looking for a woman. f4m is a woman looking for a man. m4m is a man looking for a man, f4f a woman looking for a woman. The letters are gender, not orientation, and the tag describes tonight's search rather than an identity you are stuck with. A bisexual man might post m4f in one room and m4m in another, and nobody considers that a contradiction.
The full set you will actually meet
Beyond the four basics, a handful of letters do most of the remaining work.
A means anyone or any gender. f4a is a woman open to anybody, a4a is anyone seeking anyone, which is the tag of someone who is genuinely just here to talk to whoever is interesting. T means trans. t4t is trans seeking trans and is one of the most-used tags online, precisely because it names a preference for shared experience rather than for a body type. m4t and t4m exist too. NB or enby covers non-binary, so nb4a is common. C means couple, so mf4f is a mixed couple looking for a woman, mf4m the same looking for a man, and c4c is a couple looking for another couple.
Extras get bolted on after the tag rather than inside it. Age and region are the usual pair, giving "m4f 30s uk". Then the mode: "long term", "one scene", "chat first", "rp only". Those trailing words carry more useful information than the letters do, and the people who add them get better answers.
Where the tags came from
They come from personals listings, the classified-ad format where every post needed a headline that could be scanned in a list of thousands. Craigslist made the format famous, the boards and forums that followed inherited it, and it spread into chat rooms because it solves the same problem: too many people, not enough screen, and no time to ask everyone individually.
That origin explains the style. A tag is a headline, not a conversation. It belongs at the front of your line, not as your entire line, which is the single most common mistake newcomers make with it. "m4f" on its own is the personals equivalent of a blank advert.
How to read a room that uses them
Scan the left side to know who is speaking and the right side to know whether you are being spoken to. If the right side does not include you, the message is not addressed to you, and there is no insult in that. A tag is a preference stated politely up front so that nobody wastes an hour finding out.
Which brings up the rule that matters most: a tag says what someone wants, never what they are owed. Posting m4f does not create an obligation on any woman in the room, and pressing someone whose tag does not match you is how a conversation ends and occasionally how an account ends. The room rules are unsentimental about it. On the same subject, share what is yours to share, and never post a partner's or an ex's photos without their consent, whatever your tag says.
Using them well
Lead with the tag, then give a sentence that sounds like a human being. "f4m, late twenties, and I would rather write something slow than sprint at it" tells a reader three useful things and gives them a hook. Compare that with a bare "f4m" and you can see why one gets answered.
Keep the right side broader than you think you should. A specific list narrows your night dramatically, and an age range plus a gender is usually enough. Do not stack the tag with demands, since "m4f 18-25 only, must send pics first" is four rejections in one line. If you want the longer version of that argument with examples, what to say first in a chat room puts good and bad openers side by side, and why nobody replies explains the arithmetic behind the silence.
Where each tag tends to land here
The tags are room-agnostic but they cluster. People posting m4f and f4m mostly end up in the main room and in the hunt for a sexting partner. m4m traffic runs through gay chat, f4f through lesbian chat, and anyone whose tag moves around depending on the night will recognise bi chat. t4t and t4a belong to trans chat, which is moderated hard against fetishisation, and a4a suits queer chat or the main room equally.
Roleplayers use the same grammar for characters rather than for themselves, which is worth stating explicitly when you post so nobody misreads it. Finding roleplay partners covers the etiquette. In kink rooms the tag usually gets a role bolted onto it, as in "m4f, dom", and at that point the role is doing more work than the letters. The kink partner guide and the specific hunts for a dom, a sub, a domme or a switch all use that longer form. Couples posting mf4f and c4c usually want the swinger room.
If the acronyms are new to you, the other one you will meet immediately is on the ASL page, and your first time in a chat room walks through the rest. Post a tag, add a sentence, and let the room sort itself.