The Hot Posts metric in the Post Performance table is a metric provided by Facebook. You can change the columns displayed in the table to include or exclude this metric for Facebook Pages.
Hot Posts let you identify high-performing content at a glance. These trending posts are good recommendations for boosting.
Facebook’s definition for Hot Posts is ‘whether the post is currently hot (popular). Based on whether the total actions as a percentage of reach exceeds a certain threshold.’ In other words, Facebook looks at the average engagement rates for content on each Page, and then uses a standard deviation to flag the posts with relatively high engagement rates.
Once a post is flagged as hot, its status will not change over time.
You can Boost Hot Posts at your own convenience or with an automatic trigger. To learn more about this, take a look here.