- Core Module should only be imported onces in the AppMdule, no other feature moduel should import it, reason being- Core Module contains all the core component which are present in all the pages (like- header, footer, sidenave, nav, advertisment section etc) so- these core component should be there only in app.comp.html page but not in another module's comp
- Shared Module will be present in all the feature module as well the AppModule