Means Helpers / Supporters. These were the Aus and Khazraj pagans of Madina who responded to Muhammad's call to Islam and offered him protection and a centre of piratical and terroristic operations against all those whom he perceived as his enemies.
Contrary to all the Muhammadan misinformation and disinformation, the Ansar were intimately related to the Judaised Arab tribes in the Madina, the Banu Nadir, Quraiza and Qaynuqa.
The geneaologies of these tribes were intertwined to such a degree that al Akhtal satirized the son of Hassan b Thabit by calling the Ansar of Banu al Najjar, Jews. This was the same tribe to which Muhammad's maternal relations belonged.