Views are the V in MVC. They are the visual part of the application. Typically, a web app renders HTML pages, meaning HTML views. A view is a template that consists of a mix of HTML and possibly some server-side content.
ASP.NET Core uses view engines to actually render the views, an extensible mechanism. Before the time of Core, there were several view engines available; although their purpose was always to generate HTML, they offered subtle differences in terms of syntax and the features they supported. Currently, ASP.NET Core only includes one view engine, called Razor, as the other one that used to be available, Web Forms, was dropped. Razor has been around for quite some time and has been improved in the process of adding it to ASP.NET Core.
Razor files have the cshtml extension (for C# HTML) and, by convention, are kept in a folder called Views underneath the application, and under a folder with the name of the controller to which they apply...