Worldcon, or more formally The World Science Fiction Convention, is a science fiction convention held each year since 1939 (except for the years 1942 to 1945, during World War II). It is the annual convention of the World Science Fiction Society (or WSFS). The members of each Worldcon are the members of WSFS and vote both to select the site of the Worldcon two years later and (since 1955) to select the winners of the Hugo Awards, which are presented at the convention.
Read more about Worldcon: Activities, Awards, Guests of Honor, World Science Fiction Society, Convention Committees