Ubuntu 20.04 -- What are "stale online ext4 metadata check snapshots"

[mahesh]

Hi,
I've gotten some great suggestions on this forum so far, so I hope you won't mind if I ask yet another question about a code line that I found today in the system log of my Lenovo x230i with an Ubuntu 20.04 OS, desktop -- no server.

I have not come across this particular code line before and would appreciate it if someone could explain what the following line means

     b]Code:[/b]
 

Code Select Expand

Starting Remove Stale Online ext4 Metadata Check Snapshots
I have come across this line in other people's logs posted online, but no one seems to have broken down what 1/ the function is of this removal, 2/ what exactly is being removed and 3/ why.

Also, very importantly, 4/ what am I to understand by the word *online* in this code line?

The sender of the code line was systemd.

Anyone care to explain this ? Thanks.