Dear Foxbravo03 -
Our friend Jhooper gave it to you - for USA... But I see you are in Ireland.
Dont have the Shannon or Dublin approaches handy.
But I will give it to you the Irish ATC way...
"Clear to (descend) 4,000 feet, transition level 50, QNH is 1007 hPa..."
At 5,000 feet (TRLVL 50) the pilots will reset their altimeter to 1007.
Transition level vary just about everywhere, in USA, it is 180...