A costume party or fancy dress party is a type of party, common in contemporary Western culture, in which many of the guests are dressed in costume, usually depicting a fictional or stock character, or historical figure. Such parties are popular in the United States, United Kingdom, Canada, Australia, Ireland and New Zealand, especially during Halloween.

A party is a gathering of people who have been invited by a host for the purposes of socializing, conversation, recreation, or as part of a festival or other commemoration or celebration of a special occasion. A party will often feature food and beverages, and often conversation, music, dancing, or other forms of entertainment.