What is the difference between a transition state and an intermediate? ... ?

An intermediate is an unstable and short-lived molecule in a reaction which is formed in between the reaction when reactants change into products.

Whereas, transition state is just the state before formation of a new molecule. A n intermediate differs from a transition state in that the intermediate has a discrete lifetime. A transition state last for just one bond vibration cycle. Intermediates may be highly stable or unstable molecules.