What exactly is Snap or Flatpack ?

I feel like I have been living under a rock for the the last decade
whenever people mention /snap/ and /flatpack/.

1) Are they the same idea as /kubernetes/, and if not, then what is
   *that*?
2) What is the difference between them (other than that they are two
   incompatible brands, like /apt/ and /yum/ (aka /dnf/) are functionally
   the same thing, but incompatible with each other)?

Is it just packaging the executable with all the libraries it references
and a wrapper that sets up paths to those libraries, or is there a
virtual machine involved?

Do these wrapped applications see the full file system, or is there a
shell game of /chroot/ and links or loopback mounts to break out?

At 74 I am old, but I hope to still learn some new things!