Conventions are added meanings of bridge bids which convey
information about the hand of the bidding player. These
conventions allow players a rough idea of what cards other
players have, and often allow a partnership to bid exactly the
number of tricks they will take.  See Standard American Yellow
Card.  A gathering of people with similar interests or goals.
I've been to science fiction/fantasy conventions and cognitive
science conventions and I have to say that the former are a lot
more fun.  At cognitive science conventions, people give talks
about cognition all day long and then mingle with one another at
night to try to catch up with colleagues and network. I suspect
that there is also a lot of trying to get laid going on, but
it's all beneath the surface.  At science fiction/fantasy
conventions, some people hold panel discussions about various
topics related (sometimes only tangentially) to SF, some people
watch anime, and some people just hang out in the con suite.
There's usually a masquerade and a da