Ball是“球”，park是“公园、场地”，number是“数字”。这个短语是什么意思呢？请看对话：

    A: Nice shirt. How much did you pay for it? I’d like to buy one for my dad.

    B: I forgot the exact price, but I can give you a ball park number, like, US$50.

    Note: “Ball park” is an American colloquialism originally referring to the playing field of the game of baseball, the American national pastime. In baseball, one of the most exciting spectacles is the home run, when the ball is hit so hard that it travels all the way to the stands, that is, out of the playing area. If a number is within the ball park, that means it’s close to the right price, and we call it a ball park number. So the idiom refers to an average or expected number usually used in pricing. If a number is out of the ball park, it is off the mark by a big margin.