A 308 redirect, also known as a "permanent redirect", is a type of HTTP status code used to indicate that a requested resource has been permanently moved to another location. It is similar to a 301 redirect, which is also used for permanent redirects, but with one crucial difference: 308 redirects ensure that the request method used for the original request is also used for redirecting the request.

When a browser sends a request for a specific URL, the web server checks the status code of that URL. If the status code is 308, the browser sends a request to the new location specified in the redirect, but retains the original request method, whether it is GET, POST, PUT, DELETE, etc. This is useful when you are forwarding a form or other method that should not be changed during forwarding.

A 308 redirect is useful for search engines because it allows them to recognise that the redirect is permanent and that the new location replaces the original URL. This prevents the search engines from indexing the original URL and transferring the entire ranking and link value to the new URL.

It is worth noting that 308 forwarding was introduced in HTTP/1.1 and is not supported by all web servers or browsers, but it is a recommended method for permanent redirects that should retain the original request method.

Overall, a 308 redirect is a useful tool for website owners and developers when a permanent redirect is needed but the request method must be maintained. It helps to maintain consistency for the user and transfer the overall ranking and link value for search engines to the new URL.