I first saw this
term in a long list of parties thrown in honor of a
couple getting married. My first thought was to wonder what kind of
sick bastards were getting hitched this time. A
Google search for the term yields some interesting results, to say the least, and I've yet to summon up the bravery to try it on an
image search.
After a bit of research, however, I found that a 'pounding party' in this context isn't nearly as dirty as it sounds. It is simply a party given to welcome newcomers to a community, where the guests each bring them a pound of different things that they may need in their homes, such as a pound of sugar, a pound of coffee, or a pound of nails.
I will pointedly refrain from mentioning the other context this term is used in.