[kosta50]

Orthodox Churches that use the Old Calendar are Russian, Serbian, Jerusalem and monasteries on Mt. Athos. They are in full communion with the See of Constantinople. Other Orthodox Churches (Greek, Romanian, Bulgarian, Ukrainian, etc.) are also in communion with Constaninople.

Various so-called Greek Catholic churches, Uniates, are not Orthodox churches, Alexandria and similar monophysite, the Maronite Church and so on, are in communion with Rome since the 15th century (following the so-called "re-union" in Florence).

Orthodox Churches are those churches that are in communion with the See of Constantiople. Others are either heretic churches that broke off early in Christian history, or those that joined the Roman Carholic Church at a later date by accepting Latin theological innovations.

[The_Reader_David]

Actually "Greek Old Calendar Churches" could refer to the Greeks who went into schism from the Church of Greece over the adoption of the New Calendar. In which case, they are certainly not in communion with Rome as the objection to the New Calendar was in part that it was adopted to move the feasts of the Orthodox to coincide with those of heretics (that is papists).

[NYer]

Various so-called Greek Catholic churches, Uniates, are not Orthodox churches, Alexandria and similar monophysite, the Maronite Church and so on, are in communion with Rome since the 15th century

Just a point of information. The Maronite Catholic Church has never separated from Rome. They are one of only two Eastern Catholic Rite churches that have maintained fidelity to the Magisterium from the very beginning.