PageSpeed Insights (PSI) measures the performance of a page on both mobile and desktop devices and then provides suggestions to improve that page.
Lighthouse has powered PageSpeed Insights since the end of 2018. This means that the results in your PSI reports are based on the Lighthouse API.
When scanning a page, PageSpeed provides two types of data: Lab and Field.
Lab data is collected in a controlled environment with predefined devices and network settings. It effectively debugs performance issues, and its testing can be easily reproduced. However, it might fail in catching real-world bottlenecks.
On the other hand, field data (also called Real User Monitoring or RUM) includes performance data coming from real page loads. It’s effective to capture true, real-world user experience, but the set of metrics and its debugging potential is limited.