Google PageSpeed is a family of tools by Google, designed to help webmasters improve their website's performance. PageSpeed Insights is an online tool which helps in identifying performance best practices on any given website, provides suggestions on a webpage’s optimizations, and suggests overall ideas of how to make a website faster.
Per URL request, it grades webpage performance on a scale from 1 to 100
Lab data is performance data collected within a controlled environment with predefined device and network settings. This offers reproducible results and debugging capabilities to help identify, isolate, and fix performance issues.
Opportunities provide suggestions how to improve the page’s performance metrics. Each suggestion in this section estimates how much faster the page will load if the improvement is implemented.
Diagnostics provide additional information about how a page adheres to best practices for web development.
Use fast hosting, a fast DNS (‘domain name system’) provider
Minimise ‘HTTP requests - keep the use of scripts and plugins to a minimum, use one CSS stylesheet (the code which is used to tell a website browser how to display your website) instead of multiple CSS stylesheets or inline CSS
Ensure your image files are as small as possible (without being too pixelated)
If your pages are slow to load, Google will figure it out and will categorize your website as poor user experience, therefore suffering in terms of organic visibility. If you haven't done it yet, I strongly advise you to use the PageSpeed Insights tool: Google PageSpeed Insights
Please note that Lighthouse belongs to Google and their advice is (a bit too) specific to Google Chrome, so for instance it will advise you to use new image formats which may not be usable and rendered on other browser such as Firefox or Safari.
Lighthouse is a great tool to chek Performance. Pageload time is key in SEO and has a massive impact on rankings.