ष is one of the Devanagari consonants. Its sound in IPA is /ʂ/. This word does not exist in Perso-Arabic alphabets, Pashto alphabets, etc., but many people use the Arabic letter Sin(س) with four dots above (ݜ) to represent the Devanagari letter ष.
Usage
This letter is not used mostly in Hindi-Urdu, but it is used in Sanskrit. In Urdu or Perso-Arabic script, there is no consonant to represent this letter, but many people use the Arabic consonant Sin with four dots above (ݜ).
References
ष Wikipedia(Text) CC BY-SA