In the .Net world if you were to create a web application historically you’d be developing the full stack: web pages, an API (of sorts), business logic and database.
As JavaScript MV* frameworks have become more prevalent a .Net web dev may use one of these frameworks, such as Angular or Knockout, to create a the UI but often will still be creating the rest of the stack.
As part of learning more and more about JavaScript I’ve come across the concept of “No Backend” or “backend as a service” where a company may provide all the server side functionality you might need (different companies often offering different levels/types of services).