The "POST" method is an HTTP request used to send data to a server for processing. It is commonly used when submitting form data or uploading files. Unlike the "GET" method, which appends data to the URL, POST sends data in the body of the request, making it more suitable for larger amounts of data and sensitive information. When a client sends a POST request, the server processes the data and typically returns a response indicating the result of the operation. This method is essential for creating and updating resources on the web, making it a fundamental part of web development and APIs.