Jivatman, rooh, embodied soul etc. are different words used in different religions/cultures to speak of the localised divine presence.
Svetasvatara Upanishad – Chap 5 Mantra 9 is as follows:
vālāgraśatabhāgasya śatadhā kalpitasya ca
bhāgo jīvaḥ sa vijñeyaḥ sa cānantyāya kalpate
The above means, “Know the embodied soul to be a part of the 100th part of the point of a hair divided a 100 times; and yet it is infinite.”
From modern perspective, there is nothing physical known within the body that can be called as, “subtle body” or embodied soul so if we do not take the above literally, the implied meaning of the above appears to be that if we try to discover embodied soul, it is apparently very difficult to discover it, so in that respect it is subtle. But, since it is reflection of Atman/Consciousness/Self, actually it has infinite presence. We know that mind is not a physical thing and it has the imagination to be anywhere. So, mind can broadly be called Jivatman**. Although consciousness is everywhere, when it is associated with the physical bodies, it gets individualised and one feels oneself separate from the Self. Just like in a room there are various radio signals that are detected by various radios to different degree, consciousness is detected by different bodies to different degree. Be it stone, plant, animal or human or empty space, consciousness is everywhere and is detected to a different degree by different things/beings.
One can think of mind as made of several layers. The outermost layer of mind is where we mostly live, that is waking conscious state, the next layer is subconscious state, the next is unconscious state. All these states happen on a screen or a background. Most of us are not aware of this background as we identify ourselves with body-mind. This background of the mind can be considered as consciousness. It can only be reached when there are no thoughts in the mind and the identification with body-mind ceases.
*Different religions may use different terms and explanations.
**Ramana Maharshi says, “What is called ‘mind’ is a wondrous power residing in the Self. It causes all thoughts to arise. Apart from thoughts, there is no such thing as mind. Therefore, thought is the nature of mind. Apart from thoughts, there is no independent entity called the world. In deep sleep there are no thoughts, and there is no world. In the states of waking and dream, there are thoughts, and there is a world also. Just as the spider emits the thread (of the web) out of itself and again withdraws it into itself, likewise the mind projects the world out of itself and again resolves it into itself. When the mind comes out of the Self, the world appears. Therefore, when the world appears (to be real), the Self does not appear; and when the Self appears (shines) the world does not appear. When one persistently inquires into the nature of the mind, the mind will end leaving the Self (as the residue). What is referred to as the Self is the Atman. The mind always exists only in dependence on something gross; it cannot stay alone. It is the mind that is called the subtle body or the soul (jiva).”