UK finance jargon - in plain English
Whether your loan is backed by an asset the lender can take if you stop paying.
Secured debt is borrowing tied to an asset, usually your home. If you stop paying, the lender can repossess that asset to recover what they are owed. Mortgages are the most common example. Unsecured debt has no asset attached. The lender cannot automatically take your property if you miss payments, but they can take legal action to recover the money. Credit cards, personal loans, and overdrafts are all unsecured. Because unsecured lending carries more risk for the lender, it typically comes with higher interest rates.
Your mortgage is secured on your home. Miss enough payments and the lender can begin repossession proceedings. A personal loan for a holiday is unsecured. If you stop paying, the lender will pursue you through debt collection and potentially the courts, but they cannot take your house for that loan specifically.
Secured loans can sometimes offer larger amounts and lower rates, but the risk to you is greater. Never secure a debt against your home unless you fully understand the consequences of not repaying.
People take out secured loans to consolidate unsecured debt without realising they have just put their home on the line for what was previously lower-stakes borrowing.