A Heroku application is a collection of processes that run on the Heroku dyno manifold. Whether you are running a local process or a remote one on a distributed cluster of machines, a Heroku application is essentially a set of processes, each consuming resources like a normal UNIX process.

To add flexibility and have better control over how you define your process configuration, Heroku defines the concept of process type. Each process that you run as a dyno can be classified as a web process or a worker process type depending on whether it handles HTTP requests or does some background processing. You could also define a custom process type to add flexibility to your application definition.