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.