A security deposit is a refundable amount of money you provide to open your secured credit card account. It acts as collateral—meaning it protects the lender in case you can't make your payments. Because the deposit reduces the lender's risk, it can allow you to get approved for a credit card even if you have no U.S. credit history.
You may already be familiar with security deposits from everyday life:
Renting an apartment: Landlord may holds a deposit in case of damage or unpaid rent
Setting up utilities: Company may require a deposit if you're a new customer
Cell phone plans: Carrier may ask for a deposit if you have no credit history
Renting a car or staying at a hotel: A temporary hold may be placed in case of damage or extra charges
In each case, the deposit is returned when everything goes well.