Yā Hussain is an Arabic phrase used by Shia Muslims to invoke the memory or intervention of Hussain ibn Ali. It is especially used in the context of the Mourning of Muharram.
The British in colonial India heard Muslims chanting "Yā Hussain! Yā Hassan!" (a reference to Hasan ibn Ali, brother of Hussain) during the Mourning of Muharram, and approximated it as "Hobson-Jobson", which became a term referring to the similar derivation of an English equivalent for a foreign-language words by adapting English words or names that have a superficial resemblance in sound.
During unrest following the release of official election returns in Iran in 2009, supporters of Mir-Hossein Mousavi conjoined his name with that of Hussain ibn Ali by chanting "Yā Hussain! Mir-Hossein!".