How do a tax return and a tax rebate differ from each other?

A tax return is an official document you submit to HMRC detailing your annual earnings and work-related expenses. Think of it as an income-expenditure ledger.
On the other hand, a tax rebate is what you get when you've overpaid your tax. It's the government's way of saying, "Oops, you've paid us too much! Here's what we owe you."