There is something, invisible to physical eyes, that emanated or wrap the physical body of every living being.
People call this with many different names, Aura, Prana, Chi, Qi,
It's more of electro magnetically like kind of energy.
There is a very simple technique to test it's existence, by putting the palm of your hands close to each others.

And then as you focusing your mind on your palm, you can start to feel a 'gel' like electromagnetic field that exist between your palm, although you might not be able to see it using your physical eyes.
I found people are generally do have the capability to 'feel' the aura, both of themselves or others.
But some people do able to 'see' the aura and describing it as 'dynamic energetic field' with changing color.

Just like any other magnetic field, it has vibration. Thus frequency.
The vibrational frequency of the aura is tightly correlated with the being's emotional state and character.
That's why people often said something like "I sense very bad vibe from that person"...
It means that their vibrational frequency of their aura do not match / resonate with each other.
Every thing that you thought of, think, sense and feel will have an 'impact' to your own aura.
Hatred, Anger, Fear, Sadness, Guilt, Pride, Acceptance, Compassion, Love, Joy, Peace will have it's own effect on your overall aura vibrational frequency.
There is a great classic work, written in early 20th century which discuss this 'field' in great detail.
Man Visible and Invisible by C.W. Leadbeater
https://b-ok.cc/book/2491552/b65c6eThe practice of Yoga, Qigong, Taichi is a practice that contains exercises / techniques that work on this specific electro-magnetically aspect of human body with goal to balanced it.
And some traditions also use the same energetic field for 'martial art'.
https://youtu.be/Ban5TwkSBSQ?t=33