what a (something)

What a ___" communicates the idea "That's really ___" or "You're really ___." Here are some examples:

If you have to throw away food that's still good, you can say:

What a waste, huh?

Here's something a woman can say when a man opens a door for her:

What a gentleman! Thank you very much.

If a lot of people show up to your event or party:

What a great turnout!

Wow!

"Wow!" expresses excitement. You say it when someone tells you something or shows you something. You can use "wow" to express a variety of emotions about the thing you're being told or shown:

• it's interesting and exciting
• you want to encourage the person, especially a child
• you can't think of anything else to say

a performance

The word “perform” means to sing, dance, act, play a sport, or do something else that requires skill. 

When someone does one of those activities, you can talk about what they did as “a performance”:

I saw an amazing dance performance on Saturday.

A: What did you do after your performance?

B: Nothing, actually, I just went home and went straight to bed.