Feature modules are NgModules for the purpose of organizing code.
As your app grows, you can organize code relevant for a specific feature. This helps apply clear boundaries for features. With feature modules, you can keep code related to a specific functionality or feature separate from other code. Delineating areas of your app helps with collaboration between developers and teams, separating directives, and managing the size of the root module.
https://angular.io/guide/feature-modules
The purpose of a NgModule is to declare each thing you create in Angular,
and group them together (like Java packages or PHP / C# namespaces).
There is two kind of main structures:
- “declarations” is for things you’ll use in your templates: mainly components (~ views: the classes displaying data), but also directives and pipes,
- “providers” is for services (~ models: the classes getting and handling data).
Source: Understanding Angular modules (NgModule) and their scopes
From angular official docs:
Modules are a great way to organize an application and extend it with capabilities from external libraries.
Angular libraries are NgModules, such as FormsModule, HttpClientModule, and RouterModule. Many third-party libraries are available as NgModules such as Material Design, Ionic, and AngularFire2.
NgModules consolidate components, directives, and pipes into cohesive blocks of functionality, each focused on a feature area, application business domain, workflow, or common collection of utilities.
Modules can also add services to the application. Such services might be internally developed, like something you’d develop yourself or come from outside sources, such as the Angular router and HTTP client.
Modules can be loaded eagerly when the application starts or lazy loaded asynchronously by the router.
NgModule metadata does the following:
- Declares which components, directives, and pipes belong to the module.
- Makes some of those components, directives, and pipes public so that other module’s component templates can use them.
- Imports other modules with the components, directives, and pipes that components in the current module need.
- Provides services that the other application components can use.
Every Angular app has at least one module, the root module. You bootstrap that module to launch the application.
The root module is all you need in a simple application with a few components. As the app grows, you refactor the root module into feature modules that represent collections of related functionality. You then import these modules into the root module.
Read more here: https://angular.io/guide/ngmodules