Symfony in Drupal 8 changes the structre to MVC with the help of symfony. Symfony is a open source framework. Its created in object oriented concepts.
HttpFoundation and HttpKernel HttpKernel is the Symfony component. The all the web intractions is start from the request, and its end with response. The function of HttpKernel is converting the request in to response.The HttpKernel is attach with event listeners. The name of each of the "kernel" events is defined as a constant on the KernelEvents class. Every event has their own objects like kernel.request, kernel.controller, kernel.view, kernel.response,kernel.finish_request,kernel.terminate, kernel.exception ;
EventDispatcher The EventDispatcher is the central point of Symfony's event listener system. The EventDispatcher is changed some invoked hooks.Its allows to your application communicate with ech other by dispatching and listening them.
YAML The Symfony YAML components parses convert YAML string to PHP arrays and virse-versa. Human friendly data serialization standard for all programming languages.
ClassLoader ClassLoader from sysmfony components. Class loader is autoloader for class files. Class loader Implement PSR-0 class loader. Its loads only classes of a specific namespace or all namespaces.
Routing 3 Parts in Routing section. They are RouteCollection, RequestContext and UrlMatcher.The route collection means defining routes, RequestContext means information about the request and UrlMatcher is pointg request to route.