A Future contract falls under the category of Derivatives and not a Security, as by definition the value of Derivation is solely decided by the underlying security, and in this case, the value of the Future contract depends solely upon the underlying stock or commodity.
Futures Contracts-
A Futures contract falls under the category of Derivatives as it has the underlying Asset as a Security. Any Future contracts price fluctuates with the change in the price of the underlying security making it different from a Security.
By definition a Derivative is a secondary Security whose value or price is solely decided by the underlying security hence Futures come under the category of Derivatives as the Value of a Futures contract depends solely upon the value of the underlying stock or commodity. This makes Futures a derivative and not a security. The right to exercise or Buy/Sell the underlying security is with the Holder of the Future contract but there is a Legal obligation of Physical delivery if the Futures contract is held till expiry.