The "X-Content-Type-Options" is an HTTP response header used by web servers to prevent browsers from interpreting files as a different content type than what is specified. By setting this header to "nosniff," it instructs the browser to strictly adhere to the declared content type, reducing the risk of executing malicious scripts. This security measure is particularly important for protecting against attacks like Cross-Site Scripting (XSS). When a server sends this header, it helps ensure that users only receive content that is safe and intended, thereby enhancing the overall security of web applications.