A keysigning party is a way to bring a lot of people together to sign each other's keys
Sign keys first, then party... ;)
Bob gets the fingerprint for his key to send to the party coordinator:
[bob@yohost bob]$ gpg --fingerprint bob
pub 1024D/9004BC23 2003-01-29 Bob Smith (User Bob)
Key fingerprint = FC62 5CF4 8A83 4B10 54BA 8D40 DB58 668A 9004 BC23
sub 1024g/B5577FFB 2003-01-29
While at the party, bob will get a list of fingerprints for other people's keys, and verify the identity of those people using driver's licenses, passports, or other trustworthy photo identification
When bob gets home, he can download all the keys, verify the fingerprints, and sign the keys. Then he sends them back up to the keyserver. Voila! bob has signed keys and has had other people sign his key!
Now bob is going to sleep off his hangover. What a party!