Please explain “ball park number” in this sentence: He said he forgot the exact price for the T-shirt, but gave me a ball park number, like, 30 dollars. My comments: He forgot exactly how much he paid ...

Please explain “ball park number” in this sentence: He said he forgot the exact price for the T-shirt, but gave me a ball park number, like, 30 dollars. My comments: He forgot exactly how much he paid ...