The "Shared" folder in an ASP.NET Core MVC project typically contains the shared Razor views like layout and error pages. These views can be reused across multiple pages, providing a consistent look and feel to the application.

When a user is not authorized to access a specific action, ASP.NET Core returns a default HTTP status code of 401 Unauthorized. This status code indicates that the request lacks proper authentication credentials or the provided credentials are invalid for the requested resource. It's a fundamental part of the authentication and authorization process in web applications.

Georeplication is a strategy that ensures high availability by deploying application instances in different geographical regions. This approach minimizes downtime in case of regional outages or disasters, providing a robust and fault-tolerant architecture.

ASP.NET Core's approach to preventing Cross-Site Request Forgery (CSRF) attacks involves using a token named CSRF (Cross-Site Request Forgery). This token is generated for each user session and is included in requests to ensure that the request originated from the same site, thereby preventing malicious actions from other domains. It's an essential security measure in web applications.

ASP.NET Core's configuration system allows you to access configuration values using a key/value API. This system can be configured using multiple configuration sources (e.g., JSON, XML, environment variables, command-line arguments) to provide flexibility in managing application settings.

When you see a generic "An error occurred" message during development, it might be because Debug Mode is disabled in your ASP.NET Core application. Enabling Debug Mode provides detailed error information to help developers diagnose issues.

For reusability, developers can create Razor Components, which are similar to partial views but with more logic encapsulation. Razor Components encapsulate both the UI and the code, making them highly reusable and self-contained.

To make a tag helper available across all your Razor views without adding its namespace to each view individually, you can use the element in the _ViewImports.cshtml file. This centralizes tag helper configuration for the entire directory, making it accessible to all views within that directory.

The "Startup.cs" file in an ASP.NET Core project plays a crucial role in configuring middleware and services for the application. It defines how the application will handle requests, set up routing, and configure various components like authentication, logging, and dependency injection. It's essentially the entry point for configuring the application's behavior.

ASP.NET Core introduces a built-in Dependency Injection (DI) system, which was not part of traditional ASP.NET. In the past, developers often relied on third-party libraries for DI, but ASP.NET Core brings this critical feature into the framework, making it easier to manage dependencies in your applications.