The Keep-Alive Test tool checks whether keep-alive (persistent HTTP connection) is enabled on the server where the website is hosted.
Keep-Alive is a method that allow web browser (client) to access multiple files (requests) from server in one Transmission Control Protocol (TCP) connection instead of new connection for every file (request). Keepalive also called persistent HTTP connection.
Keep-Alive helps conserve network resource by using single connection per client. Also it reduces network congestion and decreases latency. Hence, enabling keep-alive helps improve pagespeed of the website.
You can easily enable keep-alive on your website to improve site speed. If your site is on WordPress, you can enable keep-alive with or without using a plugin. Learn how to enable keep-alive.