Difference between a void contract and a voidable one

  1. What is the difference between a void contract and a voidable one? 2. What are the elements necessary to support a claim of undue influence and provide examples. 3. What is an illegal contract? Why do courts refuse to enforce contracts (or bargains) made by competent adults if the contracts harm no third party but are illegal? 4. What is the purpose of the Statute of Frauds?