Basically, if you either start a line with four spaces, or use backticks (these: `) to encase text, the formatting will treat it as program code, which means it'll remove any automatic line breaks due to running out of space on your screen, which is very useful when discussing program code, and extremely unhelpful for any kind of other writing, as you'd have to scroll sideways for however long any sentence (or set of sentences) goes on until you start a new line again, which quickly gets annoying, especially on mobile phones.

As an example of what I'm talking about:

This is what happens if you start a line with four leading spaces.
I can do this for multiple lines, and I only ever get a new line if I  
press  
the  
enter key.  
However, if I start writing and writing without that, and just type out a very long run-on sentence, it quickly becomes unreadable, which is also what happened to your initial post above.

As for the other option to get similar formatting, backticks around textallow you to dump a bit of special formatting right in the middle of text, and both have the added benefit of ignoring all the other special formatting things Reddit usually does, which can be useful under certain circumstances as well.

And here I thought it was going to be either this (marked NSFW primarily for implications) or that S(?)lay the dragon comic that I can't find right now.

Also, semi-related: Shirokuma Tensei (=Reborn as a Polar Bear)

Not exactly the same, since the person wasn't a bear before, but I think it could fit.