Even Wiki has a different definition than Val, not sure where she is coming from, Mohammad is the last messenger of God and therefore inspired and infallible:

Islam is an Abrahamic monotheistic religion which professes that there is only one and incomparable God (Allah) and that Muhammad is the last messenger of God. It is the world's second-largest religion, and the fastest-growing major religion in the world, with over 1.8 billion followers or 24.1% of the global population, known as Muslims. Muslims make up a majority of the population in 49 countries. Islam teaches that God is merciful, all-powerful, unique, and has guided mankind through prophets, revealed scriptures and natural signs. The primary scriptures of Islam are the Quran, viewed by Muslims as the verbatim word of God, and the teachings and normative example 

A Muslim is someone who follows or practices Islam - Wiki