The best word to describe these events.
I am often hired to shoot themed parties, concerts, and contests at different clubs around the country. Some social clubs have us shoot weekend parties in Vegas or New York, while others have us photograph the occasional house party down the street.
I relax, have fun with the party goers, but always maintain being professional.
I post the images on a locked gallery and provide the host with the password that he/she can hand out to the revelers.