“Thank you all for coming. Wow, what a great turnout.”

You organized an event for people who want to practice giving speeches in English. A lot of people came to the event. Now you're going to welcome everyone and introduce the first speaker. The first thing you say is:

Thank you all for coming. Wow, what a great turnout.

Thank you all for coming.

You can say this at the beginning of a meeting, a business party, a wedding, etc. if you are the leader or organizer of the event.

what a (something)

The sentence "What a great turnout" means "There was a great turnout." In general, the expression "What a ___" communicates the idea "That's 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.

a (good/great/nice) turnout

The "turnout" to an event means the number of people that come to it. Here are some examples:

Are you coming tonight? We're expecting a decent turnout.

Voter turnout for the last election was the highest it's been since the mid-'60s.

You can use "turnout" to refer to the number of people who come to:

• a conference
• an election
• a charity event

But you wouldn't talk about how many people came to work or to a regular class with the word "turnout". For things that happen regularly like that, you'd talk about "attendance" instead:

Attendance has been down for the past couple of weeks because of that flu that's been going around.