What exactly is "other" on extended storage?

[Raidou Kuzunoha XIV]

I know the "other" data folder on the system storage is often the download/upload notifications, or sometimes DLC or what not for games that are otherwise stored on the external. But I've never been able to figure out what the "other" folder on the extended HDD actually is.

 

I noticed today after updating my PS4 to 8.01, I randomly gained about 8gb of extra free space on my external HDD. Last I checked earlier in the week, I definitely had less free space, and have not deleted anything since (or gotten any updates). Kinda weird, I almost never see the free space fluctuate on the external unless there's been an update for a game or I'm actively installing/deleting something. I noticed the "other" folder is now 42mb, when I could have sworn it was a few gigs last I checked, so I assume that, maybe, the "other" section got semi-wiped after the system update somehow. I used to think that maybe the "other" was also DLC/updates for a game that was otherwise stored on the internal HDD, but now I'm not so sure. No matter what anyway, I can never seem to get rid of the "other" section completely.

 

Does anyone know what it is exactly? I've tried searching, but most of it is specific to the internal HDD/system storage, and there's a lot of speculation there as well.

 

I'm a bit paranoid with my external HDD right now because I just had one go bad on me recently, so I hope the extra space gained isn't that it deleted a game or something. I've gone through everything and I don't notice anything missing, but I have about 200+ games installed right now so something could very well have just gone unnoticed. Didn't notice anything else weird though, no "HDD was incorrectly shut down and needs to be repaired" messages or anything either, so hopefully it's fine. Checked the SMART stats on my PC as well and it all seems good.