A convention is a gathering of individuals who meet at a pre-arranged place and time in order to discuss or engage in some common interest. The most common conventions are based upon fandom, industry, and profession. Fan conventions usually feature sales, people dressed up as their favorite characters, and guest celebrities. Trade conventions typically focus on a particular industry or industry segment, and feature keynote speakers, vendor displays, and other information and activities of interest to the event organizers and attendees. Professional conventions focus on issues of concern to the profession and advancements in the profession. Such conventions are generally organized by societies dedicated to promotion of the topic of interest.
In politics, a political convention is a meeting of a political party typically to select party candidates. A constitutional convention is a special meeting to amend or draft a constitution.
In any form of art there are conventions that may simply be expectations (for example, that paintings are rectangular) or stock devices (a comedy ends with a marriage, but a cowboy film can end with the hero riding off into the sunset). There are generic conventions that are tied very closely to a particular genre - and may even help to define what it is.