Wiktionary
n. (context legal English) The right of a lender to take possession of collateral offered to secure the loan.
WordNet
n. any interest in a property that secures the payment of an obligation
Wikipedia
A security interest is a type of property interest created by agreement or by operation of law over assets to secure the performance of an obligation, usually the payment of a debt. It gives the beneficiary of the security interest certain preferential rights in the disposition of secured assets. Such rights vary according to the type of security interest, but in most cases, a holder of the security interest is entitled to seize, and usually sell, the property to discharge the debt that the security interest secures.
Usage examples of "security interest".
The President decides what is or is not in the country's security interest as part of his executive powers.
What's at stake - Horton's life, or some larger national security interest?
As such, we could argue that we had a legitimate Silesian security interest in investigating Hecate's actions and intentions.
So that I could pledge a security interest in the ship during out-system trading.