What does "ghayb" (the unseen) refer to in this verse?

Imām Ibn al-Jawzī (d. 597/1201) summarized the scholars' opinions in his book "Zād al-Masīr" as follows:

1. Revelation. [Ibn ʿAbbās, Ibn Jurayj]
2. The Qurʾān. [Abū Razīn al-ʿUqaylī, Zirr ibn Ḥubaysh]
3. Allāh the Almighty. [ʿAṭāʾ, Saʿīd ibn Jubayr]
4. What is hidden from the servants concerning matters of Paradise, Hell, and similar topics mentioned in the Qurʾān. [Al-Suddī from his teachers, Abū al-ʿĀliyah, Qatādah]
5. What Allāh has predestined. [Al-Zuhrī]
6. It means belief in the Messenger (Muḥammad ﷺ) for those who did not see him in person. ʿAmr ibn Murrah reported that the companions of Ibn Masʿūd said to him, "Congratulations! You fought alongside the Messenger of Allah (ﷺ) and sat in his company." He responded, "The status of the Messenger of Allah (ﷺ) was evident to those who saw him. However, what is more astonishing is a people who believe in him based on encountering a written book (the Qurʾān) without seeing him." Then he recited the verse: "Those who believe in the unseen..." (2:3).