Al-Haqqah is one of the names of the Day of Judgement, because during it the promise and the threat will inevitably occur. Due to this, Allah has declared the greatness of this matter. So He says,

﴿وَمَآ أَدْرَاكَ مَا الْحَاقَّةُ ﴾

(And what will make you know what Al-Haqqah is)