Everything in the original writeup is correct. I am adding a few things.
First, the etymology of the term. The Yiddish term is best transliterated 'shnorer', and it comes from Middle High German snurren, to hum or whir. This apparently comes from the sounds of the musical instruments played by beggars.
I believe that the term is also used in a semi-technical sense to describe the men who circulate at orthodox social events (bar mitzvahs and the like), collecting money for various causes. Their behavior is seen as being basically a shakedown, as the participants are under a kind of obligation to share the joy of the event, so they are forced to give. These semi-pro schnorrers receive a commission, which may be a large cut of the funds they raise. Given that we're working on Yiddish terms here, call it a