Old-school British approval meaning very good, well done, or sounds great. It’s polite, a bit posh, and usually said with a wink, like you’re cosplaying a tweed jacket in a period drama. People use it seriously sometimes, but it often lands best as cheeky praise when something actually goes right.
"Got the contract signed and the boss didn’t have a meltdown. Jolly good. Now nip to the pub, grab a cheeky pint, and pretend we’re not all skint till payday"