In Dart, the `@Deprecated` annotation is used to mark code elements (such as classes, methods, fields, or parameters) as deprecated. It serves as a documentation tool to indicate that a particular element is no longer recommended for use and may be removed or replaced in future versions of the code or library.

When a code element is marked with `@Deprecated`, it generates a warning or error at compile-time, notifying developers that they are using deprecated code. This helps prevent accidental usage of deprecated elements and encourages developers to migrate to alternative or updated code.

Here's an example of how to use the `@Deprecated` annotation in Dart:

class DeprecatedClass {
  @Deprecated('This class is deprecated. Use NewClass instead.')
  void deprecatedMethod() {
    // Deprecated method implementation
  }
}

void main() {
  DeprecatedClass deprecatedInstance = DeprecatedClass();
  deprecatedInstance.deprecatedMethod(); // Generates a warning or error
}​

In the example above, the `deprecatedMethod()` in the `DeprecatedClass` is marked as deprecated using the `@Deprecated` annotation. The annotation includes an optional string parameter that provides a deprecation message explaining why the element is deprecated and suggests an alternative.

When the `deprecatedMethod()` is called in the `main()` function, it generates a warning or error depending on the configuration. The warning or error message will include the deprecation message specified in the `@Deprecated` annotation, indicating that the method is deprecated and suggesting the use of an alternative.

By using the `@Deprecated` annotation effectively, developers can communicate the deprecation of certain code elements and provide guidance on how to migrate to newer or recommended alternatives. This helps maintain code quality, encourages codebase evolution, and informs other developers about potential changes in the API.