A default happens when a lender decides you're not going to be able to pay back what you've borrowed. This can be because you miss too many payments or don't make your payments in full. A default usually means that your account is closed.
Repossession is when a lender takes back what you offered as security on a loan – this could be a house, car, sofa or a cell phone – when you default on an account.
How these affect your score
Both defaults and repossessions can affect your credit score negatively, as they show you're unreliable when it comes to paying back what you borrowed.