Irish colloquial term of endearment.
A good, obliging fellow...
One who has a cheery demeanour and who will help out where he can. Would mostly be used by older generation towards someone a good many years their junior. Can be used in a patronising manner, towards one of your peers.
"There's a good gossom" says Jim as he pats his mate John on the arse, after he walked sheepishly into the room with a tray of tea for all the lads, having lost a bet...