What does extension-provided configuration mean in Config Snapshot? Configuration Snapshot enables snapshotting of extension-provided
  configuration. It's used by Configuration Synchronizer to support
  updating configuration provided by modules, themes, and the install
  profile.


Recently I checked my database and found there are two tables
config
and 
config_snapshot
I found that the module Config Snapshot creates the table config_snapshot table
While reading through project page text,I see it says "it enables snapshotting of extension-provided configuration"
What does extension-provided configuration mean ?
As commented by Clive,


  “Extension” seems just to be being used as a catch-all term for
  modules, themes and installation profiles. Those three are the only
  things that can provide config outside of core, so it seems a safe bet