Valuable consideration is the legal term for the economic value that would be derived from any contract on one side or the other. In order for a contract to be valid, it must have a beneficial nature to one party; such a beneficial nature is considered in an economic context, and therefore valuable consideration is the amount of money that is listed as the subject in a contract.
If a contract was disputed in court and either side could show that there was no valuable consideration within the contract, then it would be deemed null and void.