Welcome to English in a Minute,where we teach you all about idioms in American English.Let's pretend you are in a major U.S.city.You are listening to an American English conversation,and you hear this:
A:Hey,Bob.Ever since you opened your coffee shop,you have been very busy.Is the bussiness going well and making money?
B:Yeah! I can't believe it.It's going really well.In fact,my coffee shop has become a real cash cow for me.
How does a cow produce cash?Everyone knows cows make milk.But in American English,a "cash cow" is a product or service that makes a lot of money for a bussiness.This common phrase is used in casual and business conversations.And when you use is ,everyone will understand what you are saying.
And that's English in a Minute.