Web performance is all about improving the speed availability of your website, including making slow processes seem fast.
Speed refers to how fast your site can be loaded when a request is made from a web browser. Availability can also be referred to as uptime or reliability and refers to the percentage of time that your site can be accessed.
Faster website download speeds have been shown to increase visitor retention and loyalty and user satisfaction, especially for users with slow internet connections and those on mobile devices.
Web performance optimization (WPO), or website optimization is the field of knowledge about increasing web performance.
References
The “why” of web performance