Page Speed is a metric that measures the speed of a website. It measures errors, network speed, server response time, file size, and how well the site loads.
Page Speed is used to measure the performance of websites. Page speed is often confused with the 'site speed', that is, the various sample of page views.
In general, Page speed is defined as the "time to first byte" or the "page loading time". Page speed measures how long it will take for the browser to show the first batch of information. The page speed can be affected by various page elements like its HTML code, CSS that styles page elements, various JavaScript files, images, videos and other multimedia, etc.
Page Speed important for SEO because
The first update by Google on page speed as the ranking factor was rolled out in 2010. However, it wasn't considered of much importance at that time. A decade later, Google took page speed strictly and used separate mobile and desktop speed metrics.
In 2017, Google announced they would give mobile site speed even more consideration than before and rank websites based on how fast they load for mobile users. Thus, they introduced the Accelerated Mobile Pages or AMP.
According to the Kissmetrics survey, if a page load time is longer than 3 seconds, the users are more likely to bounce back to look for a different result. And, the search engine considers the bounce rate as one of the most damaging aspects of SEO.