Waterfall model is one type of software process model.

So there is no difference between the two but they share a

parent-child relationship.

A software process model is used in software engineering and

it encompasses a set of activities, methods, actions, tasks

and products.

A waterfall models is a linear model that suggests a

systematic, sequential approach to develop a software

starting from communication with the client and passing

through planning, modeling, construction to the deployment,

delivery and feedback.