Intercommunion

In Christianity, full communion is a relationship of understanding among different Christian denominations that they share certain essential principles of Christianity. Views vary among denominations on exactly what constitutes full communion, but typically when two or more denominations are in full communion it enables services and celebrations to be shared among congregants or clergy of any of them with the full approval of each.

Full communion is an ecclesiological term for an established relationship between Christian denominations that may be constituted by shared eucharist, doctrine, and ecclesiology. Different denominations emphasize different aspects or define the term differently.

For the Orthodox Church, the Catholic Church, the Oriental Orthodox churches and the Church of the East, full communion exists only between Christians who form a single church. In a weaker understanding of the phrase, "full communion" is instead a matter of practical relationship between denominations that fully retain their distinct identities.

As a practical matter for most Catholics, this affects whether or not a member of one Church may partake of the Eucharist celebrated in another, and for priests, whether or not they may concelebrate the Eucharist with priests of another Church. In each case, if the two Churches are in full communion, then they may.

For certain people taking up an office in their community in the name of the church, a specific "profession of faith" is required, demonstrating that they are in full communion with the Catholic Church, even if they have been members of a separate church whose sacraments the Catholic Church considers to be valid. Being "in full communion with the Catholic Church" requires that they "firmly accept" its teaching on faith and morals.

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Wikipedia