What is the meaning of consciousness?
How its meaning is different from the meaning of soul?
You are asking a difficult question, which takes us to the very essence and origin of life.
Yogananda, as the ancient yogis do, teaches that all creation emanates out of consciousness. God is consciousness. That pure consciousness in yogic tradition has three attributes: sat-chit-ananda, which Yogananda translated as ever existing; ever conscious; ever-new bliss.
Swami Kriyananda begins his book Superconsciousness with these words: "Consciousness, in its pure state, is absolute: more absolute than the speed of light, which slows on entering a material medium such as the earth’s atmosphere; more absolute than the existence of matter, which is only a manifestation of energy; more absolute than energy, which is itself a vibration of consciousness."
Once he mentioned: "You can’t define consciousness." In other words, "You can’t define God." Once you define it, it is not pure consciousness anymore. So consciousness can’t really be defined, it simply is. However, it is not empty: in it lies total bliss.
You can go to the dictionary and find that the word comes from the Latin con-scius, which means "knowing with," or "that with which you know." But it needs to be clear that consciousness is not the mind, it is completely above thinking. Consciousness in its pure state doesn’t do anything. Again, it simply is: above all space, time, and movement.
The soul is the individualized consciousness of God, like a wave of the sea. It is nothing (no-thing) but pure consciousness, nothing but sat-chit-ananda.
Peel an onion and what remains? Nothing (no-thing). Similarly, strip yourself of all superficial layers, all self-definitions, and what remains? Pure being, pure awareness, pure existence: consciousness. That is Self- or Soul-realization, which leads to God realization: "Behind the wave of my consciousness is the ocean of Cosmic Consciousness." (Yogananda)
It is very enlightening to meditate on this teaching of Swami Kriyananda, from his book Affirmations for Self-Healing:
"Man needs to learn to change his focus from what he is aware of to what he is aware with."
So meditate on what you are aware with: that is consciousness. Consciousness is the perceiver, or as Yogananda also says "the soul is the observer." This is the source, this is who you are, this is what God is, this is what the world is made of.
Words can only explain so much. I think Yogananda might advise you: "Meditate! It is the only way to find the answer to your question. The mind will never fully understand the true nature of consciousness. But formless bliss will teach you."
In God’s friendship,