A web stack is like a pile of books. The top element is the application with which the user can interact, while the bottom element is the base: the operating system. The other elements in between are the technology necessary for both the application and the operating system to communicate with each other. They all form a team with a common goal: to provide everything the application may need to work.

If you are totally new to web development, coming from another field of programming or learning from scratch, you need to know the difference between the two major worlds of the web: frontend and backend. Although they are totally different, sometimes they can overlap.