I thought stuff like "Explain Like I'm Five" and "AMA" was proprietary to the community, or at least the Reddit community, not Reddit as a company.

I checked and I found at least those subreddit forum names were registered as trademarks.

• TODAY I LEARNED (TIL)
• SHOWERTHOUGHTS
• EXPLAIN LIKE I'M FIVE
• NOSLEEP
• AM I THE ASSHOLE?
• IAMA
• RPAN (actual subreddit name is R/PAN but they messed up the word mark for the registration I think.)
• ASK REDDIT (makes sense since this includes Reddit's name.)
• NATURE IS FUCKING LIT (I thought you couldn't register word marks with swearing but I guess I'm wrong. Must be only for offensive terms then...)
• ASK ME ANYTHING (yes somehow this "generic term" is a trademark now...")
• AMA
• ELI5

Also they have some trademark registration applications for WALLSTREETBETS that have not been finalized yet.