When Consideration Becomes Illusory: Debating Between Illusory Promise and Voidable Contract

Yaar samajh nahi aaya, please help. While studying Contract Law for DU LLB Entrance, I'm getting my head spun by two similar concepts - Illusory Promise and Voidable Contract. Both seem to deal with situations where consideration is not real, but I'm finding it difficult to differentiate between them. In an Illusory Promise, a party makes an offer which leaves it entirely in their discretion to accept or reject, rendering the promise illusory. But isn't that similar to a Voidable Contract, where consideration is absent or illusory, making it voidable at the instance of the aggrieved party? Are they not the same thing? Or is it just a matter of perspective? Can someone please explain the distinction?