Did you really meet Namie Amuro?

Someone told me:

• × I met Namie Amuro!

The intended meaning was this:

• 安室奈美恵に会ったことがある。

Meeting someone means the two of you shook hands, exchanged business cards, had an introductory conversation, or something like that. Here's the correct version:

• ○ I saw Namie Amuro in person on the street!

"In person" means in the physical presence of someone or something. Look at Space Alc's definition; their example sentence is almost exactly the same situation.

• in person〔映画｛えいが｝やテレビではなく〕じかに、生で
• I saw a famous actor in person at the restaurant the other day. : 先日そのレストランで有名な俳優を直に見ましたよ。

Here's another example:

• A: Should I give him the bad news by email?
• B: No, it would be better to tell him in person.

"On the street" could be substituted with "in a cafe", "in a convenience store", or any other place. The reason to include it in the sentence is to emphasize that when you saw her, it wasn't at one of her concerts.

I remember the first time I saw a local celebrity in person when I was a kid. It was one of the weathermen from a local TV station. I was surprised by how much thinner he looked in person than on TV. It turns out that the harsh studio lights eliminate the shadows on people's faces, making them look heavier than they actually are.