Ummah (أمة) is an Arabic and Islamic word that means "community" or nation. It is often used to mean the nation of the believers (Ummah Al-Muhmini) in Islam, i.e the whole muslim world.

The phrase al-ummatun wahid in the Quran (the One Community) refers to all of the muslim world unified. The Constitution of Medina, negotiated by Muhammad(P) and accepted by the Mala [Senate] of Medina, explicitly refers to Jewish and pagan citizens of the Medina Republic as members of the Ummah or nation [1] http://www.dawn.com/2001/07/20/op.htm#1 . So when modern Islamists use the term "The Islamic / Muslim Ummah" they mean to refer to all the people in the lands & countries where predominantly muslims reside, where the Khilafah state once ruled, including non-muslims minorities. When they talk of unifying the "Islamic Ummah" they would include these non-muslims, as citizens of the Islamic Ummah, living peacfully with thier own respective religions, paying less tax (called Jizya) than muslims, being loyal citizens of the Khilafah state.