Page Speed Insight is an online tool by Google developers to check how your website performing regarding it’s speed, it check whether a site follows Google speed guidelines. Based on several speed affecting factors, page speed insight give score to each page for mobile loading as well as desktop. This score is given out of hundred. If your website follow every guidelines, then your score should be 100 out of 100.
From 2010 Google start to consider site speed as a ranking factor in their algorithm. Beginning it was a small factor which affect less than 1% search queries. But now it should be a strong factor because Google is focusing more on happier customers than keyword density and meta tags. Actually Google is no more looking into your meta keyword and description, but still people spending more time to make their meta richer. May be investing these time for optimizing your page speed will give you more returns in search rank.