I'm not Orthodox myself, but in the book His Broken Body, the author says that while there is no official term in the Orthodox church for "Church penitent" or "purgatory," because there is no official dogma concerning these ideas, the concept nevertheless, practically, exists:
It is certain that Eastern Orthodox theologians do not use (and do not like) the word purgatory, mainly because they are concerned with its legalistic implications, the historical connection with the doctrine of indulgences and other possible misunderstandings... The Eastern Orthodox problem with 'purgatory' is not so much the idea of mercy after death as the legal concepts, terminology and dogmatization used to express it.
We can certainly affirm that Orthodox Christians hope and believe that prayers for the dead are, however mysteriously, effectual. But it is also very important to admit that this conviction is based more on apparition stories than on specific scriptural evidence. The beloved Dialogues of Pope Gregory the Great are famous for such stories, but there are many similar examples in contemporary Orthodox literature.
The author than sites examples of stories from Prologue from Ochrid and Eternal Mysteries beyond the Grave, before concluding
Such stories remind us that popular Orthodox theology has a version of purgatory that is hardly distinguishable from its Roman Catholic counterpart... The fact that Christians have always prayed for the dead comes with the unshakable certainty that the practice is indeed efficacious.