Final answer:
An 'illusory promise' is a commitment where the person making the promise retains the choice to follow through or not, making it insufficient for creating a binding contract.
Step-by-step explanation:
When a person promises that they may do something if they want to, they have made an illusory promise. Such a promise is considered to lack real commitment or obligation and hence is not sufficient consideration for a contract. In contract law, consideration refers to something of value that is exchanged between parties and is necessary for a valid contract. An illusory promise suggests that the party who made the promise retains the choice to follow through or not, rendering the promise without a binding contractual obligation.