The [HttpDelete] attribute in a .NET Core API is used to specify that an action method should handle HTTP DELETE requests. This attribute is significant because it:

Verb-Based Routing: Signifies that the decorated action method should be triggered when the API receives an HTTP DELETE request for the specified route. This is part of verb-based routing in ASP.NET Core, which allows you to define different actions for different HTTP methods (GET, POST, PUT, DELETE, etc.).

HTTP Semantics: Enforces adherence to the HTTP semantics for DELETE requests. It ensures that the action is specifically designed to handle deletion operations, promoting a more RESTful and standards-compliant API.

Self-Documenting: Provides self-documenting code, making it clear to other developers and API consumers that the action is intended for resource deletion.

Action Selection: Helps the routing system choose the correct action method to execute based on the HTTP verb in the request. This is especially important when you have multiple action methods with different HTTP verb attributes in the same controller.

Resource Deletion: Indicates that the action method is responsible for deleting or removing resources on the server, often identified by a route parameter or query parameter.

Overall, the [HttpDelete] attribute is significant because it helps maintain the clarity and consistency of your API, aligns with HTTP standards, and enables proper resource deletion through DELETE requests.