It's a number between 0 - 1200 that represents the history of all your dealings with loans, credit cards, mortgages as well as phone and electricity bills.
When you apply for a loan, the bank or lender uses your credit score to work out how "risky" you are as a borrower and then decide if it's a yay or nay.
But wait, there's more: Even after you've been approved for a loan, your credit score can still impact the amount you can borrow, as well as the interest rate you pay (AKA the amount you have to pay each month).
Bored from this overview? Watch this 1 min video.