A Muslim, also spelled Moslem, is an adherent of Islam, a monotheistic, Abrahamic religion based on the Quran, which Muslims consider the verbatim word of God as revealed to prophet Muhammad. "Muslim" is the Arabic term for "one who submits to God".
Muslims believe that God is one and incomparable. Muslims also believe that Islam is the complete and universal version of a primordial faith that was revealed at many times and places before, including through the prophets Abraham, Moses and Jesus. Muslims maintain that previous messages and revelations have been partially changed or corrupted over time, but consider the Quran to be both unaltered and the final revelation from God—Final Testament.
Most Muslims accept as a Muslim anyone who has publicly pronounced the Shahadah (declaration of faith) which states, "I testify that there is none worthy of worship except God and I testify that Muhammad is a Messenger of God." Their religious practices include daily prayers (salat), fasting during Ramadan (sawm), almsgiving (zakat), and the pilgrimage to Mecca (hajj) at least once in a lifetime.
Currently, the most up-to-date reports from an American think tank and PBS have estimated 1.2 to 1.57 billion Muslims populate the world, or about 20% of an estimated 2009 world population of 6.8 billion, with 60% in Asia and 20% of Muslims living in the Middle East and North Africa.
Source: Wikipedia, "Muslim", available under the CC-BY-SA License.