The document discusses different classifications of contracts according to their legal validity and enforceability under Indian law. It defines valid, voidable, void, unenforceable, and illegal contracts. A valid contract meets all legal requirements, such as offer, acceptance, lawful consideration and capacity to contract. A voidable contract is valid until avoided due to issues like duress or misrepresentation. A void contract becomes invalid due to reasons like impossibility of performance. An unenforceable contract suffers from technical defects like improper stamping, but can become enforceable by rectifying defects. An illegal contract has an unlawful object like murder and cannot be enforced by law.