Does OP mean “original poster” or “original post”?

Solution 1:

People all over the Internet have asked the same thing—which, on the face of it, suggests that different forum posters (and perhaps, in some cases, the same people at different times) have used it to mean both things.

For example:

Does OP mean Original Post or Original Poster or both? (AnandTech, posted January 7, 2005)

Does OP mean the original post or poster? (Physics Forums, posted January 3, 2008)

Does OP stand for "Opening Post," or "Opening Poster?" (Kongregate, posted May 7, 2011)

What does OP mean? (Meta Stack Exchange, posted September 10, 2012)

Noob Question: What does OP mean? (World of Warcraft Forums, posted September 15, 2012)

what does op mean? (League of Legends Forum, posted January 3, 2013)

OP -- Original Post or Original Poster? (The Straight Dope, posted December 12, 2016)

If you examine these various discussions, you'll see that, typically, someone will say that OP stands for original poster, and then someone else will say that it stands for original post, and then someone else will say that it can be used to mean either thing, and then someone else will suggest that it stands for something off the wall like Otto Preminger or Opossum Party.

At English Language & Usage, I think, most longtime participants use OP as an abbreviation of original poster, but not everyone follows this convention all the time.

Perhaps the most neutral, descriptivist handling of the abbreviation that I've come across is the one in Daniel Chandler & ‎Rod Munday, A Dictionary of Social Media (Oxford, 2016):

op 1. (OP) In online forums, short for original poster (who started a thread) or original post (the message that started it).

Solution 2:

I'm not really sure who is qualified to say that one use or another of this abbreviation is "correct" or "incorrect". But I have certainly used "OP" to stand for "original post" instead of "original poster". The Oxford Dictionaries entry for "OP" gives this as a possible meaning:

(in online forums or comment pages) original post (or poster).

It also gives the following relevant example sentence:

• ‘Oops, upon closer inspection of the OP, I see you weren't looking for a "blame" song.’

Solution 3:

Either or an abstraction related to both, depending on context.

To be clear, "OP" may refer to:

• the Original Post; or

• the Original Poster; or

• the Original Post or the Original Poster, ambiguously;

• the Original Post and the Original Poster, abstractly.

When it's ambiguous, the writer may be thinking of the post or the poster. They may fail to specify which for a variety of reasons, ranging from believing that the definition normally refers to the one that they intend to simply not caring to specify.

However, others mean "OP" abstractly as "the original source of the content". They're not actually referring to either the post or the poster specifically, so we can't say that their usage of "OP" maps to one over the other.

The distinction between this abstraction and ambiguity is the presence-or-absence of referential transparency. For example, "laugh out loud" may be the etymology of "LOL", but "LOL" isn't an acronym for it, such that substituting one for the other would change the meaning of a text.

Likewise, "OP" may have an ambiguous etymology and often refer to either the post or the poster in some cases, but there's also a separate definition distinct from these. It'd be most precise to say that this separate definition is distinct from either of its etymologies, much like "LOL" is distinct from "laugh out loud".