According to Islam there is different definitions, between a Messenger and a Prophet. Some are both but all are Prophets.
A Messenger delivers a new message or book with law and it ordered to convey it, Like Moses
A Prophet backs up the previous message but is not ordered with sacred law. Like Soleman, David.
They are free from major and minor wrong action or sin before and after Prophethood. We do not accept that our prophets can commit sins.
They are truthful before and after message and are people free from anything that people who dislike, in terms of the physical side. Muhammad (peace and blessings be upon him) was known as the truthful, the trustworthy before prophethood.
They have miracles and revelation from God that backs up their claim.