An ETag is a signature attached a server response. If the client requests a URL (HTML page, image, style sheet, etc.) whose ETag is identical to the one it already has, the web server will reply that it does not need to download the resource and that it should use the one it already possesses. Using ETags saves huge amounts of bandwidth.

If a page only needs to be changed twice a year, use a static page built outside of the CMS. This reduces CPU usage, bandwidth and electricity consumption.
That is because dynamic content management systems must load the various software layers to serve the content requested by the user — e.g. the HTTP server, applications server, content storage system (database) — and, potentially, related cache systems. On the other hand, a static file is directly read and sent to the user by the HTTP or cache server, skipping the need for the application server or database.