Areas are some of the most important components of ASP.NET MVC projects. The main use of Areas are to physically partition web project in separate units. If you look into an ASP.NET MVC project, logical components like Model, Controller, and the View are kept physically in different folders, and ASP.NET MVC uses naming conventions to create the relationship between these components. Problems start when you have a relatively big application to implement. For instance, if you are implementing an E-Commerce application with multiple business units, such as Checkout, Billing, and Search etc. Each of these units have their own logical components views, controllers, and models. In this scenario, you can use ASP.NET MVC Areas to physically partition the business components in the same project.
In short, an area can be defined as: Smaller functional units in an ASP.NET MVC project with its own set of controllers, views, and models.