Collateral is an asset or assets offered by a borrower in order to procure a loan. Should the borrower default on his payment(s), the lender would take possession of the collateral, which may then be sold to recoup the lender's losses.
Technically, collateral could be any asset, though typically it takes the form of personal property, investment securities, or real estate, the values of which can be readily determined.
Other terms in common use in the market are"margin", "margin asset" and "margin agreement" and similar terms using "credit support" instead of "collateral" or "margin," collateral", "collateral asset" and"collateral agreement." 
When a lender offers a loan against collateral offered by the borrower, the lender is said to take a security interest in the collateral. 
14c., "accompanying," also "descended from the same stock," "side by side, "together" "parallel, along the side of" 16c., "colleague, associate." Meaning "thing given as security" is from 1832, Amer.Eng., from plrase collateral security (1720).