"Show counts on browser icon" - What does this mean?

I came across this option when I was changing some interface settings. What does it do exactly? What are “counts?”

‘Counts’ means the number of unread notifications and private messages.

They show up on your avatar, e.g. one notification:

If you check “Show counts on browser icon”, then those counts will show up on your browser tab as well. So if you have several tabs open, you can see if there’s been a notification on the SDMB tab without going there to check.