Both collateral and security refers to the sitaution when a secondary obligation is created in order to secure the primary obligation.
Collateral is a general term signifying the concept that a secondary obligation is provided to ensure the performance of the primary obligation. It may not be used in the plural since it is not a specific right but the description of a legal concept.
On the other hand, security is a legal instrument for securing an obligation. It may take various forms and it is also used for specific security instruments of a certain kind.
