A shnorrer is a beggar or freeloader in Yiddish. Fundraisers and, occasionally, rabbis are professional shnorrers, persuading others to stump up for good causes. Shnorrer is often used disparagingly, as in your family will do anything to shnorrer an invitation for a free meal.
But sometimes it is used with grudging admiration. The shnorrer was supposedly a beloved character in the shtetl, living off his wits and conveying a feeling of dignified entitlement to the fruits of his begging. Perhaps this says something about the importance of tzedakah, charity, in traditional communities. The shnorrer was doing a public service by giving others the chance to fulfil the mitzvah. That said, it is better to support yourself than to be a shnorrer (Maimonides, Laws of Gifts to the Poor, 10:18).
Shnorrer comes from the Yiddish shnorn, meaning to beg, and is apparently related to the Middle High German shnurren, meaning to hum. Theres a famous Jewish joke in which Moishe the shnorrer is outraged to hear that his wealthy patron has halved his annual allowance. The donor apologetically explains that his son has married a woman of expensive tastes and he, the father, must foot the bill. He can marry who he wants, retorts the shnorrer. Just not with my money.