What is the Difference Between ROCOR-MP and ROCOR-A (ROCA) What differentiates the various synods within the Russian Orthodox Church Outside of Russia aka ROCOR?
I met someone who stated that their particular synod was in communion with ROCOR-A (ROCA), but not ROCOR-MP, because the latter was in communion with Moscow and Constantinople.
A quick google search told me that there were in fact multiple ROCOR groups that are distinct from ROCOR-A (ROCA) and who are not in communion with ROCOR-MP. Comments on those groups would be appreciated but not necessary to answer the question.
ROCOR merged with the Moscow Patriarch (MP) in the last decade and is now referred to as either ROCOR or ROCOR-MP.
I think that ROCOR-A is identical to ROCA, which is the Russian Orthodox Church Abroad, which broke with ROCOR when the latter merged with MP. ROCA and ROCOR used the refer to the same thing, but now they refer to two distinct groups, the differences of which I would like answered in this question.
Edit - From Wikipedia:

Critics of the reunification [of ROCOR and MP] argue that &quot;the hierarchy in Moscow still has not properly addressed the issue of KGB infiltration of the church hierarchy during the Soviet period.&quot; It has also been noted that &quot;some parishes and priests of the ROCOR have always rejected the idea of a reunification with the ROC [MP] and said they would leave the ROCOR if this happened. The communion in Moscow may accelerate their departure.&quot;
The signing of the act led to yet another small schism from the ROCOR, this time taking with it Bishop Agafangel (Pashkovsky) of Odessa and Tauria, and with him some of ROCOR's parishes in the Ukraine, which refused to enter the jurisdiction of the Ukrainian Orthodox Church. Agafangel was subsequently suspended by the ROCOR synod for disobedience. Despite censure, Agafangel persisted with the support of ROCOR parishes inside and outside of the Ukraine which had also refused to submit to the Act of Canonical Communion. Agafangel subsequently ordained Bishop Andronik (Kotliaroff) with the assistance of Greek bishops from the Holy Synod in Resistance; these ordinations signified the breach between ROCOR and those who would refused communion with Moscow. At a Fifth All-Diaspora Council (composed of clergy who did not accept the Act of Canonical Communion), Bishop Agafangel was elevated to the rank of metropolitan; he now heads the Russian Orthodox Church Abroad - Provisional Supreme Church Authority (ROCA-PSCA) as Metropolitan Agafangel of New York and Eastern America.
Prior to the Russian Revolution there were two branches of Orthodoxy in Russia that I am aware of.  The first and largest was the Russian Orthodox Church (ROC) under the Moscow Patriarch (MP).  The second was a schismatic group called Old Believers (OB) that split away from the MP due to differences over Liturgical forms.  They are not relevant to the current discussion.

Until 1589, the Orthodox Church in Russia was governed by the Eastern Orthodox Patriarch of Constantinople.  In 1589, Russia was granted autonomy under its first Patriarch, Job.  Tsar Peter the Great forced the ROC to abolish the office of Patriarch in 1721 as part of his overall political reforms.  From that time until the time of the Russian Revolution, the ROC was governed by a Synod appointed by the Tsar that included both clergy and lay men (the "Most Holy Governing Synod").

One of the ironies of the Bolshevik Revolution was that it planted the seed for preservation of the Orthodox Church through Communism by ending all government involvement in the Orthodox Church.  As a result, the ROC was able to reinstate the office of Patriarch in 1917, the office having been vacant for 196 years.  

By 1922, however, the Bolsheviks had begun to seriously persecute and infiltrate the ROC.  At that time there were very large number of Russian Orthodox clergy throughout the world, especially in Palestine and Serbia.  Believing the MP to be under undue interference from the Soviet Government, a number of hierarchs in Serbia established on their own a Russian Orthodox Church Abroad (ROCA).  At some point the Russian Orthodox Church Abroad or Russian Church Abroad (ROCA) started to be called the "Russian Orthodox Church Outside of Russia" (ROCOR).

The situation with Russian Orthodox in America, as in other countries with diaspora, was complex.  For some time, individual parishes under ROCOR coexisted with parishes that remained under the MP, known as the "Metropolia".  ROCOR and the Metropolia had a tenuous communion in the United States.  

In 1970, the MP granted the Metropolia "autocephaly" in the United States, thus establishing what is today known as the Orthodox Church in America (OCA).  The validity of this autocephaly was contested by ROCOR and other jurisdictions within the Eastern Orthodox Church.

By 2001, ROCOR's concerns about government influence over the MP began to subside. In 2006, ROCUR returned to the MP, leaving the canonical status of the OCA in doubt. 

Since 2010, an Assembly of Canonical Orthodox Bishops of the United States has been working to resolve, among other things, the division between the MP and the OCA.  It should be noted, however, that the individual jurisdictions are in communion with each other, despite the disputes over administration..