Praise be to Allah, and peace and blessings be upon the Messenger of Allah.
The Qur’an and Sunnah contain a large number of names and descriptions for the Day of Resurrection. Among the most well-known are:
The Day of Resurrection, the Hour, the Last Day, Al-Haqqah (the Inevitable Reality), Al-Qari‘ah (the Striking Calamity), Al-Ghashiyah (the Overwhelming Event), As-Sakhkhah (the Deafening Blast), At-Taghabun (the Day of Mutual Loss and Gain), the Day of Gathering, the Day of Judgment, the Day of Calling One Another, the Day of Meeting, the Day of the Promised Threat, the Day of Regret, the Day of Emergence, the Day of Eternity, the Day of Return, the Day of Being Presented before Allah, the Day of the Greatest Terror, a Great Day, a Difficult Day, a Witnessed Day, the Day of Gloom and Severe Distress, the Day when secrets are tested, the Day when no soul will possess anything for another soul, the Day when eyes will stare in horror, the Day when the excuses of the wrongdoers will not benefit them, the Day when they will not speak, the Day when wealth and children will not benefit, the Day when they cannot conceal any statement from Allah, the Day that cannot be averted from Allah, the Day when there is no buying or friendship, and the Day about which there is no doubt, as well as other names and descriptions mentioned in the texts.
Some scholars have stated that the names of the Day of Resurrection number around eighty, while others have mentioned nearly one hundred. Their disagreement is not a disagreement concerning any fundamental matter of religion. Rather, it goes back to the way they count the names and whether they include descriptions and conditions among the names.
Some scholars restrict themselves to names that occur explicitly in the Qur’an and Sunnah, while others add names derived from the descriptions and events of the Day of Resurrection, such as the Day of Terror, the Day of Regret, the Day of Presentation, and similar expressions.
Therefore, it is not correct to say that the names of the Day of Resurrection are restricted to a specific number such as twenty or eighty. Rather, it has many names and descriptions according to the horrors, events, and circumstances that will occur on that great day.
The multiplicity of its names has a wisdom: every name or description points to one of the meanings associated with that tremendous day. Al-Haqqah indicates that it will certainly come to pass; Al-Qari‘ah refers to that which strikes the hearts with its terrors; the Day of Judgment refers to the judgment and separation between creation; and the Day of Regret refers to the regret that will occur on that day, and so on.
The purpose of the many names and descriptions is therefore to magnify the importance of that day, explain its terrors, and remind people to prepare for it.
In summary: There is no fixed and definitive number of names for the Day of Resurrection. Rather, it has many names established by the texts, as well as descriptions and circumstances from which scholars have derived other names. This is why they differed concerning their number.
And Allah تعالى knows best.