What does the Orthodox church consider to be the defining features of Christian meditation?

I have continued to research this question and here is the answer to the question that was so urgent to me several months ago: Orthodox prayer is indeed very different and in important ways from various forms of meditation, mantra, or even prayer in other non-Orthodox Christian sects. I this is one of the best explanations I've found and it's from Orthodox Christians:

Hierom. Adrian: One more question. Why do some people connect the Jesus Prayer to some other practices, for example, to the Hindu and Buddhist mantras and meditation? Many people do not understand the difference between those ascetic practices and the noetic Jesus Prayer, the Christian prayer.

A. I. Osipov: If we turn our attention to the essential, then the types of meditation you are talking about are reflections, internal discussions. They do not carry with them the main condition for prayer – repentance. Repentance is supplication. Supplication for what? For our sinfulness, our inadequacy, our inability to live as the Gospel commands. Prayer, as Bishop Ignatius writes, should be said with attention, awe and heartfelt contrition. These things are not required by meditation. Meditation, I repeat, is a concentrated reflection on a great variety of subjects: theological, everyday, spiritual and moral, all sorts.

There exists a very important and vital act in Christian practice – the contemplation of God. However, this also differs from the above-mentioned types of meditation. This contemplation of matters of Christian faith and life goes hand in hand with humility, correct prayer and reverent inward submission of our possible understanding of any matter to God’s will.

This is the main thing that distinguishes prayer and contemplation of God from meditation.

Now for the second thing. Turning to mantras, we enter the sphere of a teaching that is decidedly, we could say, different from the Christian or, more exactly, Orthodox teaching. Mantras, in some ways outwardly resembling prayers or rather incantational prayers, are of a completely different nature. They inherently imply belief in the effectiveness of the very words pronounced, often regardless of the understanding of their meaning. We see it in Hindu practice, for example, in Japa mantra, which calls on people to repeat a god’s name as much, as often and as quickly as possible, for the name itself purifies man and brings him to the state of Samadhi. Mantras, if you wish, are one of the elements of magic and are used in the rites of pagan mystery religions.

A similar idea was promoted by the Russian name-worshipers. However, it is not God’s Name in itself that sanctifies. The Name of God is similar to an icon: it is a link to turn our prayers to the Archetype. And human purification is accomplished not through the Name itself, but through correct prayer with God’s name uttered in it, as the Holy Fathers taught. When prayer is repeated mechanically, as many times and as quickly as possible, then it “is not prayer at all. It is dead! It is useless, harmful to the soul and insulting to God,” – as Bishop Ignatius (Brianchaninov) wrote.

Currently too, we can see this tendency to understand prayer as a mantra. Books are published which recommend saying the Jesus Prayer – “Lord Jesus Christ, have mercy on me” – a huge number of times (14,400 prayers at one go!) from the very beginning. They recommend saying it very, very quickly: 3,600 prayers per hour, that is, one prayer per second (“his tongue, like a little engine, was repeating the short Jesus Prayer non-stop”). This practice runs absolutely counter to the Holy Fathers’ experience, which says that we are to say any prayer, including the Jesus Prayer, without haste, paying attention to the words of the prayer, with awe and a feeling of repentance.

From oprelesti.ru

Once you've spent a few months finding out where to look :) there are actually a large number of resources on this topic. I would highly recommend clicking through some of the other pages on oprelesti.ru as well as the writings of Sts. Ignatius (Brianchaninov) and Theophan the Recluse. St. Paisios the Athonite also has plenty to say on the subject. This article by Archimandrite Sophrony is good as well.

Finally, for anyone more interested in the topic, I can highly recommend the book The Gurus, the Young Man, and Elder Paisios. It is an excellent source of information learned the 'hard way' through geniune, spiritual experience. God bless you all!

To those who read the scriptures, Blessed Virgin Mary was one of those who meditated. Luke 2:51 says ".... and his mother kept all these things in her heart." (RSV) . Some other editions indeed use the word "meditated on " in lieu of "kept in mind". How would Mary have meditated on the events involving Jesus ? By sitting still for long hours ? No, a humble homemaker would not have much time for that. She would have meditated while cooking food, while fetching water from the well, while sewing clothes, while mending the sandals of Jesus and while preparing home remedies for small illnesses.

As for Jesus, how did he spend forty days in the desert ? His meditation would have been of a different type, fasting and sitting still in absolute communion with the Father.

Meditation, to me, is a simple method of communication and communion with God. If different cultures have complicated the process to the extend of copyrighting some of the techniques, it is their fault.