A more thorough explanation:

An illusory promise is a type of promise that cannot be enforced because it is too vague or conditional. It is a statement that seems like an offer or agreement, but it does not actually require the person making the promise to do anything at all. This means that only one side is bound to perform, and the other side is not obligated to do anything.

One example of an illusory promise is an agreement between a seller and a buyer that states that the seller "agrees to sell all of the ice cream he wants to" to the buyer. This promise is too vague and does not specify how much ice cream the seller will actually sell to the buyer.

Another example is a promise made by an employer to an employee that they will receive a bonus "if the company does well." This promise is too conditional and does not specify what "doing well" means or how the bonus will be calculated.

These examples illustrate the concept of an illusory promise because they are promises that are too vague or conditional to be enforced. In the first example, the seller is not obligated to sell any specific amount of ice cream to the buyer, which means that the buyer cannot hold the seller accountable for not fulfilling the promise. In the second example, the employer can argue that the company did not do well enough to warrant giving the employee a bonus, which means that the employee cannot force the employer to pay the bonus.