Shaddah

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 (long) consonant. It is functionally equivalent to writing a consonant twice in the orthographies of languages such as for example Latin, Italian, Swedish, and Ancient Greek, and is rendered as such in Latin script in most schemes of Arabic transliteration, e.g. رُمّان = rummān 'pomegranate'.