The E-Tag or entity tag is part of HTTP, the protocol for the World Wide Web. It is one of several mechanisms that HTTP provides for web cache validation, and which allows a client to make conditional requests. This allows caches to be more efficient, and saves bandwidth, as a web server does not need to send a full response if the content has not changed. E-Tag can also be used for optimistic concurrency control, as a way to help prevent simultaneous updates of a resource from overwriting each other. (Wiki)
We can set the E-Tag by adding the following lines in your htaccess file.
Header unset Pragma Header unset ETag FileETag None