In Arabicscript, the vowel point for "i", appearing as a small diagonal line placed below a letter: ـِ and designating a short /i/. If the Arabic letter ي (yā’) immediately follows, it indicates a long /ī/.
From Arabicكسرة (kásra), from the primitive root كسر (kásara, “to break, fracture”).
English Wiktionary. Available under CC-BY-SA license.