Shadda vs. Tashdid — What's the Difference?

Shaddah (Arabic: شَدّة shaddah [ˈʃæd.dæ], "[sign of] emphasis", also called by the verbal noun from the same root, tashdid تشديد tashdīd "emphasis") is one of the diacritics used with the Arabic alphabet, indicating a geminated consonant. It is functionally equivalent to writing a consonant twice in the orthographies of languages like Latin, Italian, Swedish, and Ancient Greek, and is thus rendered in Latin script in most schemes of Arabic transliteration, e.g.

(linguistics) Provision of a shadda symbol for Arabic words (sometimes also for Persian, Urdu, etc.), which shows gemination of consonants.

A diacritic (◌ّ) used in the Arabic script to indicate gemination of a consonant.