In the URL /Books/Details/3, the "3" is a route parameter. Route parameters allow you to pass data from the URL to your controller actions, making it dynamic and allowing you to retrieve information specific to the value "3."

In the context of ASP.NET Core, "lightweight" refers to reduced memory usage and a small download size. ASP.NET Core is designed to use fewer system resources, making it efficient for hosting applications and reducing operational costs. This lightweight nature also allows faster startup times for applications.

The primary distinction between Visual Studio and Visual Studio Code is that Visual Studio is a full-featured integrated development environment (IDE) with a wide range of features for various types of development, whereas Visual Studio Code is a lightweight, open-source code editor with extensibility for customizing and configuring it according to the developer's needs.

Attribute routing in ASP.NET Core allows for centralized route configuration, making it easier to define routes for specific actions or controllers directly within the code using attributes. This provides a more intuitive way to specify routes and helps keep routing logic within the controllers where it belongs.

To catch all unhandled exceptions globally in an ASP.NET Core MVC application, you should configure global exception handling in the Startup.cs file using app.UseExceptionHandler("/Home/Error"). This route will handle unhandled exceptions and direct them to a specified error page.

When using client-side validation in Razor forms, the unobtrusive Validation library is frequently used in conjunction with jQuery. This library allows you to define validation rules for form fields on the client side, providing immediate feedback to users without requiring a server round-trip. It's a crucial component for building responsive and user-friendly web applications.

The .NET CLI (Command-Line Interface) is a powerful tool for building, running, and managing .NET applications without relying on a full-fledged Integrated Development Environment (IDE). It allows developers to work efficiently in the command-line environment, making it a versatile choice for various .NET development tasks.

The primary role of "_Layout.cshtml" in ASP.NET Core is to define the webpage's structure and common elements, such as the header, footer, and navigation menu. It allows for consistent layout across multiple pages in your application.

In a distributed deployment scenario, ASP.NET Core Identity uses a distributed lock mechanism to ensure that only one instance applies migrations at a time. This prevents conflicts and ensures database consistency. Allowing multiple instances to apply migrations concurrently could lead to issues such as data corruption or race conditions. While database transactions are used for consistency, they may not be sufficient for distributed deployments. ASP.NET Core Identity is designed to support distributed scenarios.

The Update-Database command, when used with Identity migrations, applies any pending migrations to update the database schema to match the current state of your Identity models. This ensures that the database structure aligns with your Identity-related code changes.

ASP.NET Core includes a built-in dependency injection (DI) container for managing application dependencies. This feature helps achieve loose coupling, maintainability, and testability in your code by allowing you to inject dependencies into classes rather than hard-coding them.

The primary purpose of the _ViewImports.cshtml file is to import namespaces that you want to use across multiple Razor views. This allows you to bring in commonly used classes, extension methods, or helpers without adding individual 'using' directives to each view, promoting maintainability and reducing redundancy.