Creep isn’t really a failure in itself, rather it is a permanent, time dependant deformation of the material. Unfortunately in many applications a permanent deformation of a component will lead to failure of the total structure; a turbine blade that has become distorted is not going to help an aircraft engine work any better!
We tend to think of solids as having a fixed shape and a sharp melting point. When they reach that point they become liquids and are then able to flow. The distinction however is not as clear cut as you might think.