What it means
A big, shouty Scottish burst of joy for when something goes right and you can't be bothered acting normal about it. Goal goes in, mate turns up with cans, you find cash in an old jacket, yaldi. It's got proper Glasgow energy, but plenty folk across Scotland know exactly what you mean.
Usage examples
"Last bus was about to leave and I legged it round the corner just in time, absolute yaldi, saved me a forty quid taxi."
"Yaldi, the rain's finally stopped, get the barbecue out before it changes its mind."
"Got the job, yaldi, drinks are on me this weekend, every single one of you is coming."
"Passed the exam on a pure fluke, yaldi, never touching that textbook again."
"They'd sold out everywhere else but the chippy still had one sausage supper left, absolute yaldi."