In Roman Catholic theology and canon law, a particular Church is any of the individual constituent ecclesial communities in full communion with the Church of Rome. These can be the local Churches mentioned in canon 368 of the Code of Canon Law: "Particular Churches, in which and from which the one and only catholic Church exists, are principally dioceses. Unless the contrary is clear, the following are equivalent to a diocese: a territorial prelature, a territorial abbacy, a vicariate apostolic, a prefecture apostolic and a permanently established apostolic administration.". Or they can be aggregations of such local Churches that share a specific liturgical, theological and canonical tradition, namely, the western Latin Rite or Latin Church and the various Eastern Rites or Eastern Churches that the Second Vatican Council’s Decree on the Catholic Eastern Churches Orientalium Ecclesiarum, 2 called "particular Churches or rites" .
The importance of communion with the Church of Rome in Catholic theology is the reason why all the particular Churches, eastern or western, in full communion with Rome are called Roman Catholic, a term also used, though never officially, to refer instead only to the Latin Rite of the Catholic Church.
The technical term “particular Church” thus has two distinct, though related, meanings. The Code of Canon Law, which is concerned with the Latin-rite Church alone, uses the term “particular Church” only in the sense of “local Church”, as in its canon 373: "It is within the competence of the supreme authority alone to establish particular Churches; once they are lawfully established, the law itself gives them juridical personality." The Code of Canons of the Eastern Churches, which is instead concerned above all with particular Churches in the second meaning, has avoiding the ambiguity of the term “particular Church” by introducing the term “autonomous Church” (in Latin, Ecclesia sui iuris), as in its canon 27: “A group of Christ’s faithful hierarchically linked in accordance with law and given express or tacit recognition by the supreme authority of the Church is in this Code called an autonomous Church.”
Communion between particular Churches has existed since the Apostles: "Among these manifold particular expressions of the saving presence of the one Church of Christ, there are to be found, from the times of the Apostles on, those entities which are in themselves Churches (32: Cf. Ac 8:1, Ac 11:22, 1 Cor 1:2, 1 Cor 16:19, Gal 1:22, Rev 2, Rev 1:8, etc.), because, although they are particular, the universal Church becomes present in them with all its essential elements (33: Cf. PONTIFICAL BIBLICAL COMMISSION, Unité et diversité dans l'Eglise, Lib. Ed. Vaticana 1989, especially, pp. 14-28.)" (Communionis Notio, 7).
Obviously, the phrase “particular Church” can also be used in a non-technical sense. If people speak of “their own particular Church”, they are not necessarily giving the phrase the precise canonical and theological meaning considered here. And if the words “particular church” refer to a building and not to a body of Christians, the meaning is, of course, completely different.