Very broadly speaking, every application on a website consists of three different types of code. These types are: feature code, infrastructure code, and reliability code.
1. Feature code
This is the code that makes up an application's features. For instance, HTML, CSS, and JavaScript may be used to create the front-end app that the end-user can interact with. This includes buttons, visual elements, and various other features.
2. Infrastructure code
As its name implies, infrastructure code relates to infrastructure configuration. This generally includes the changes and interactions necessary to maintain and manage your computing solution in order to enable your app to be fully deployed.
3. Reliability code
This code is used to manage systems that an app needs to both maintain and demonstrate reliability. This often includes application-specific automated healing systems, and telemetry and monitoring systems that have to be configured when an app is deployed to show error and performance information.