happy days
1. Literally, a period of time that is pleasant, prosperous, or happy. With the economy recovering, it looks like the happy days might finally be coming back. It is not uncommon to long for the happy days of one's youth.
2. An expression of congratulation or happiness regarding positive news or information. Primarily heard in UK, Ireland. We're all going to get a bonus at the end of the month? Happy days! John: "My work visa was finally approved yesterday." Janet: "Ah, happy days! That must be a weight off your shoulders!"
3. An informal phrase of farewell. I'll see you tomorrow, class. Happy days!