Services are not really an Angular artifact per se, but rather a very general notion representing encompassed functionality, functions, and features that your application's components may need to consume. Things such as logging, data retrieval, or virtually any calculation or lookup service, can be written as services—these services can reside within your application, or live externally from it. You can think of a service as a highly specialized class that provides some service (such as looking up the distance between two zip codes) and does it well. Just as with components, not only are there tons of third-party services you can use in your Angular applications, but you can create your own custom services. We'll learn how to do this in Chapter 12, Integrating Backend Data Services.