Hello, "Buy-in" is a colloquial phrase you hear most often in the business world. You would use it like this: "I want to show this proposal to our boss, but I need to get buy-in from my colleagues first" "I need to implement this change, but first I need buy-in from corporate headquarters" Or you could use it about personal life, like your family or friends: "I want to buy this new car, but first I need buy-in from my wife!" "I think Poland would be a great place to go on holiday with my friends, but first I need their buy-in!" You can think of "buy-in" as a colloquial phrase for "agreement", or in some usages, even "permission". Hope this helps!

"Buy-in" is similar to just splitting a cost or taking up a small fee for a good or service.