Page load is a key aspect of how a user perceives the performance of your page. See Measure Performance with the RAIL Method for more information.
This audit identifies the time at which the user feels that the primary content of the page is visible.
The lower your First Meaningful Paint score, the faster that the page appears to display its primary content.
Optimizing the Critical Rendering Path is particularly helpful towards achieving a faster First Meaningful Paint.
First Meaningful Paint is essentially the paint after which the biggest above-the-fold layout change has happened, and web fonts have loaded. See the spec to learn more: First Meaningful Paint: A Layout-Based Aproach.