Does deadline means before that day or on that day?

For example

If it says:

Deadline on November 15

It means the payment or whatever it need to be delivered...

Should be on that day (Before 16)?

Or before the 15?

The deadline is the last possible day for submission

Why? Trying to justify some of your late work? lol.

Before 16

Before the 16th. Deadline means "this day at the latest".

That day.

you can give it to your professor at 11:59 Pm as long as its the 15th. once it hits 12:00 it's the 16th and late.

It means that day before midnight.

I believe it's that day, however I usually submit or deliver whatever it is the day before.

It means you can turn it in on November 16th. There is a 24 hour grace period.