What is the meaning of the letter "Hā" or "Ḥāʾ" mentioned in the Hadiths?

The letter "Ḥāʾ" (ح) in Hadith books indicates a taḥwīl al-sanad (change of chain), meaning that the Imam moves to another shaykh through whom he narrates theith, as Imam Muslim did in his Ṣaḥīḥ. Abd al-Karīm al-Khuḍayr mentioned in his commentary on Sunan al-Tirmidhī that Imam Muslim, Abū Dāwūd, and al-Tirmidhī use this letter, but it is less frequently used by al-Bukhārī. Al-ʿIrāqī also organized other sayings regarding the meaning of the Ḥāʾ, among them that it signifies taḥwīl (change), or that it is an abbreviation of the word ṣaḥḥa (it is sound).