What is CCleaner for Android referring to by "Hidden Cache"? CCleaner for Android cleans regular cache and "hidden" cache.

What do they mean by "hidden" cache?
Other apps mention that as well, e.g. the cleaners of Avast and AVG – so it seems this isn't specific to the app. I would guess they refer to the apps' "private cache" (i.e. a cache directory inside the apps' private space in /data/data/&lt;package_name&gt;).

This developer article might give some insight. Quoting (emphasis mine):


  By default, Android Extensions adds a hidden cache function and a storage field to each container (Activity, Fragment, View or a LayoutContainer implementation) written in Kotlin. The method is pretty small so it does not increase the size of APK much.


Another insight from our sister site:


  … but other then that it's all saved on hidden cache partition.


Which suggests there's some special hidden cache partition somewhere – or the writer of that answer got it a bit wrong (which I think is the case).

A third variant: Some apps create "hidden cache folders" on the SD card. Now guess what "hidden" means here? sdcard/Android/data/&lt;some_app&gt;/.cache – a hidden directory (leading dot in the name) called .cache.

No straight answer, sorry – but my guess is it's referring either to the first or to the last of these 3 options. Highest likelyness is the latter – which seems to be confirmed by the SD Maid wiki¹:


  "Hidden caches" targets cache like files that are in non-default cache directories, e.g. videoCache, .cache.


One thing for sure: they're NOT talking about geo-caching with that 



¹ thanks to SSS for this pointer!