A muʿallaq report has one, several, or all narrators omitted consecutively from the beginning of its chain.
Abū Mūsā reports:
غَطَّى النَّبِيُّ صَلَّى اللّٰهُ عَلَيْهِ وَسَلَّمَ رُكْبَتَيْهِ حِينَ دَخَلَ عُثْمَانُ (Ṣaḥīḥ al-Bukhārī, chapter on the thigh)
Translation: The Prophet ﷺ covered both knees when ʿUthmān entered.