An enforceable contract is any legal contract which carries the force of law behind it. It is a legal agreement between two parties which is legal binding. An enforceable contract is any legal agreement between two parties which is not restricted by any laws.
Unlike an unenforceable contract, a party which has agreed to be bound by a legal contract can and will be compelled to act to fulfill the terms to which it has agreed.
A legal contract is never a void contract, though it may be a voidable contract. What was previously an enforceable contract may become unenforceable in the event laws that make the contracted act illegal are passed after the contract has been created.