Why do I appear to have lots of Snap mount points when I don't even use Snap? [duplicate]

I am a long time Ubuntu user who regularly updates my OS after a new release has been available for a while. I recently updated this laptop to 21.10, having installed incrementally from 16.10 when it was brand new.

During an idle moment I looked at the directory system under the system profiler and was surprised to see so many mount points for Snap, all with "100.00% (0.0 Byte(s) of XXX MB) and all with a mount point on /dev/loopX" see screenshot.

Whatever does this mean? I have never knowingly installed a snap application.

Edit: There is an answer to my question below which I have accepted. However if you prefer to delete the question please just go ahead and do that.

Solution 1:

Depending on your Ubuntu version and flavour some applications in your system are installed as snaps by default.

A snap is a single file which contains a filesystem (squashfs), this filesystem is mounted in a way similar to block devices and it is always mounted read-only.

Since it's mounted read-only, you can not save any data in this filesystem, it's always 100% full with 0 bytes free space available. That's what is displayed in your screenshot, usage in percent and available space in bytes.