Indeed, I think it is a loosely defined concept and refers to a variety of different experiences. Merriam-Webster tells us this:
- stupor, daze
- a sleeplike state (as of deep hypnosis) usually characterized by partly suspended animation with diminished or absent sensory and motor activity
- a state of profound abstraction or absorption
So “trance” can be used in the third sense, where it (at least according to the dictionary) might be a useful rendering of jhāna. I confess, I’m not really aware of any contexts that would really apply, but in any case, it’s clearly not completely outside the semantic spectrum of the word.
The problem is that the first meanings are far more common, and they clearly pinpoint the problem.
Think of a basic example of trance, daydreaming. You drift off, the mind becomes unfocussed, and hazy associations take over. There’s a predominance of moha, delusion: you lose self-awareness. There’s no sense of reason, of a connection between things other than associations generated in the drifting mind.
This is where mindfulness steps in. Each stage of meditation is accompanied by mindfulness, which maintains a self of reflective self-awareness, a clarity that dispells the fog of delusion.
Don’t worry about it. In the meditation itself, let go and allow it to happen. Trance is not bad, it’s just not very useful. At the end of the meditation, reflect back and see whether the mind was clear or not. If your memory is vague, or if you mind is sluggish and befogged at the end of meditation, that’s a sign you’re heading down the path of delusion.
This is a common idea, but no, this is not what “wrong samadhi” means. A state of trance is not samadhi. Look at how samadhi is defined in the suttas; it is always characterized by mindfulness and awareness. “Wrong samadhi” is indeed samadhi, it is wrong simply because it doesn’t lead to liberation.
Think about the other path factors. “Wrong view” is a kind of view; it’s not the absence of views. Of course, the absence of a view can itself be wrong (“I don’t have an opinion as to whether racism is wrong”), but this is really a kind of view about views.
Similarly, think of speech. “Wrong speech” is not the absence of speech; nor is it something that is intrinsically either right or wrong. If someone asks, “What day is it today?”, I can say “Wednesday”. Right speech! If someone asks the same question tomorrow, the same answer would be wrong speech (unless it was just a mistake.) Sometimes silence can be right speech, but in the face of injustice, silence is wrong speech.
So the meaning of the path factors, their sense of “rightness” or “wrongness” is not intrinsic, it is contextual.
When it comes to samadhi, the same thing applies. Samadhi is of course the four jhanas, and it refers to a deep meditative absorption characterized by clarity and mindfulness. Such states, when practiced in the context of the noble eightfold path, lead to liberating insight.
Wrong samadhi is not the absence of samadhi, and it is not a surrogate or counterfeit of samadhi. It is samadhi, pure and simple. However, because of the context, it has a different meaning and a different outcome.
The classic example is the practice of jhanas within the brahmanical nondual tradition, which leads to oneness with Brahma, which according to the Buddha, really means a long rebirth in a blissful realm. A Christian or an skeptic might also practice jhana within their own conceptual framework, and there is no reason they should experience what Buddhists would call liberation. A Christian doesn’t want to experience Nibbana, they want to be close to God. The outcome is shaped by the causes.
This is why all the factors of the path rely on each other, why wrong view leads to wrong samadhi, and right view leads to right samadhi.
If you wanted to describe a state of trance in the terms of the path, I’d say that it reflects a stage on the path where a meditator is developing right effort, but it is so far incomplete. Right mindfulness is still nascent, and right samadhi is over the horizon.
Indeed, I believe counting was introduced in the Visuddhimagga, or at least, that; where it became known from.
In my first book, A Swift Pair of Messengers, I show that this common assumption is not found in the suttas. The suttas do not treat samatha and vipassana as separate kinds of meditation, but rather as qualities of mind to be developed through meditation. It is only in later works like the Visuddhimagga that meditations became divided into separate categories, a regrettable development in my view.
When I first encountered the teachings of Ajahan Chah, coming from a “dry vipassana” background, I couldn’t grok how he melded the two together. It was only later that I gradually learned that is is in fact what has been taught in the suttas all along.
If at the end of the meditation you are feeling dull and heavy, you could use that observation to investigate your meditation experience further. If however, you feel bright, calm and happy/peaceful, then I think it’s safe to say that the meditation process is skillful 
I definitely have a better understanding now.
