How many types of modules present in Angular

CoreModule.ts

// core module example
import { NgModule, Optional, SkipSelf } from '@angular/core';

import { ApiService } from './services/api.service';

@NgModule({
  providers: [ ApiService ]
})
export class CoreModule {
   // do not allow to be used more than ONCE!!!
  constructor(@Optional() @SkipSelf() parent: CoreModule) {
    if (parent) {
      throw new Error(
        'Import CoreModule in the root module only!!!'
      );
    }
  }
}