Decomposition isn't really the best of words—it recalls something going bad. However, in this context, it means to split apart a service, such as our football manager application; that is, splitting it into different microservices and decoupling components that follow the Single Responsibility Principle (SRP). The SRP relies on the fact that one component does one and one thing only, and that it does very well. The following diagram gives us an idea about decomposition:

In our example, the overall application could have been designed and deployed as a monolith, where we group all of the pieces together. Of course, it would have worked well, but with a lot of drawbacks (flexibility, scalability, failure, elasticity, and so on).