A somewhat related story about why text posts on reddit are called "self posts" (copy-pasted from a thread from 5 years ago where someone asked why, linked near the top of the explanation):
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It's actually a bit of a long story, but it's kind of an interesting part of reddit's history. Some of my details are probably off, but this is how I understand it.
A long, long time ago, reddit only supported submitting links. Link submissions were pretty much exactly the same as they still are now, including having a comments page that you could go to with an address like the page we're currently on: http://www.reddit.com/r/help/comments/2bmy3l/what_does_the_s...
If you look at that address, one thing to notice is that it includes the submission's ID in base-36, which for this post is "2bmy3l". If you go to http://www.reddit.com/r/all/new and look at the links to the comments pages of the newest posts, you'll notice that their IDs are increasing. For example, at the time I'm writing this, the newest IDs are 2bo3uw, 2bo3ux, 2bo3uy.
Since the IDs are increasing, you can predict which ones are coming up. You know that the next ID after those ones should be 2bo3uz. So some person decided it would be funny if they pre-constructed a link like this: http://www.reddit.com/r/reddit.com/comments/<id>/this_post_w... and then checked which IDs were coming up, filled in the "<id>" spot with one that should be used soon, and submitted it.
If they got their timing right, they'd end up with a link post that actually went nowhere. Clicking it would just take you to its own comments page, since they had managed to predict the url that the comments page would have. This was a "self post", a post that linked to itself.
So this was a pretty neat trick, and when it was successfully pulled off for the first time, it got a whole bunch of attention. Unfortunately, reddit's never been very good at just seeing some new popular thing as a novelty and moving on. No, of course pretty much everybody wanted to get their own "self post". The majority of the new submissions to the site were suddenly just people trying to make a self post, completely drowning out all the real submissions.
It was causing a gigantic mess, so one of the admins at the time decided to get people to stop by taking all the fun out of the game. They made it so that you could just choose to make a self post. You didn't have to guess the ID or anything, you just selected that you wanted to make a self post and automatically got one. It didn't have the option to add additional text or anything yet (that came later), it was just a title that linked to its own comments page.
So that's how self posts came about, and where the name originated. A quick solution to a mess being made by users that eventually turned into one of the most important pieces of reddit.
Vaguely related: I noticed that the old reddit UI would display self posts as "self.subredditname" and link posts to foo.com as "foo.com". I realized there was a potential confusion if your tld is the subreddit name, and the 2nd and only other label is "self". So I registered self.finance and posted a link to it to /r/finance .
Oh man, I remember trying (and succeeding) to do this with comments, back before you had a 30 second grace period before getting the asterisk. I wrote a comment that linked to itself.
I later became "more" famous for inadvertently DDoSing reddit, and forgot all about it until someone replied to one of my comments saying "aren't you the asshole who brought down reddit as an April fool's joke?". "Huh? No! Oh, wait".
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It's actually a bit of a long story, but it's kind of an interesting part of reddit's history. Some of my details are probably off, but this is how I understand it.
A long, long time ago, reddit only supported submitting links. Link submissions were pretty much exactly the same as they still are now, including having a comments page that you could go to with an address like the page we're currently on: http://www.reddit.com/r/help/comments/2bmy3l/what_does_the_s...
If you look at that address, one thing to notice is that it includes the submission's ID in base-36, which for this post is "2bmy3l". If you go to http://www.reddit.com/r/all/new and look at the links to the comments pages of the newest posts, you'll notice that their IDs are increasing. For example, at the time I'm writing this, the newest IDs are 2bo3uw, 2bo3ux, 2bo3uy.
Since the IDs are increasing, you can predict which ones are coming up. You know that the next ID after those ones should be 2bo3uz. So some person decided it would be funny if they pre-constructed a link like this: http://www.reddit.com/r/reddit.com/comments/<id>/this_post_w... and then checked which IDs were coming up, filled in the "<id>" spot with one that should be used soon, and submitted it.
If they got their timing right, they'd end up with a link post that actually went nowhere. Clicking it would just take you to its own comments page, since they had managed to predict the url that the comments page would have. This was a "self post", a post that linked to itself.
So this was a pretty neat trick, and when it was successfully pulled off for the first time, it got a whole bunch of attention. Unfortunately, reddit's never been very good at just seeing some new popular thing as a novelty and moving on. No, of course pretty much everybody wanted to get their own "self post". The majority of the new submissions to the site were suddenly just people trying to make a self post, completely drowning out all the real submissions.
It was causing a gigantic mess, so one of the admins at the time decided to get people to stop by taking all the fun out of the game. They made it so that you could just choose to make a self post. You didn't have to guess the ID or anything, you just selected that you wanted to make a self post and automatically got one. It didn't have the option to add additional text or anything yet (that came later), it was just a title that linked to its own comments page.
So that's how self posts came about, and where the name originated. A quick solution to a mess being made by users that eventually turned into one of the most important pieces of reddit.