Exopolitics, as the name suggests, is extraterrestrial politics. (The use of the "exo-" prefix to refer to extraterrestrial matters is already established, for example, by the term "exobiology" meaning the study of extraterrestrial life.)
Exopolitics is a direct logical extension of conventional politics to the interplanetary theatre. Dr. Alfred Webre, who formally introduced exopolitics as a discipline of study, defined it as the study of law, governance and politics in the Universe.
The need for exopolitics arises naturally. Once one accepts the existence of other sentient beings besides ourselves in our immediate neighborhood (which for the purpose of this discussion can be defined as the solar system and nearby stars), it becomes necessary to look at our neighbors politically. Like any sentient beings, they naturally have to have their own needs, desires, interests and agendas.
By analogy with political parties on Earth, which are aggregations of individuals who share a certain common political agenda, i.e., a certain set of policies they mutually seek to bring about, we can introduce the notion of an exopolitical party, which we shall define as any grouping of members of the interplanetary community with a specific exopolitical agenda, i.e., a specific set of policies toward other members of the interplanetary community.
The main job of exopolitics research then consists of identifying the existing members of our immediate neighborhood and classifying them by their exopolitical agendas, thus establishing a picture of the existing exopolitical parties in our immediate neighborhood.