What's a mendicant? It is a friar who is prohibited from owning property in common. Therefore, it is a friar or group of friars that live by begging.
These friars were organized somewhat differently from the traditional monastic orders. They were democratic, for example, rather than driven by rule. There was leadership, but the leader could come from any class, rather than only the wealthy class, as in most monasteries. Second, they actively targetted the poor; the monasteries were usually rural phenomena, and did not reach the slums of the cities. The mendicant orders emerged in the 13th century, for various reasons, but partly because of the pressures on expanding urban areas. Some preachers saw the plight of the people in these areas and wanted to direct their attention and help at those people. Third, the friars would allow lay ministers to preach.