Your energy centres are part of a subtle (unseen) system that receives and distributes energy around the body. In the Sanskrit language they are called CHAKRAS.
This term is often adopted in the western language to indicate the energy centres of the body.
Normally they are not seen in normal vision, but some people in a meditative state can visualise them and describe them as moving whirls of light that have a predominant colour. They stand out from the body at right angles and are ever moving within themselves. There are 7 colours which vary in shades according to the individual.
Red is the base centre, followed by orange,yellow green,blue,indigo and purple. Very much like the colours of the rainbow.
They transfer energy into the body and can be considered to be an intake vortex of energy. ie (universal energy,Prana, Chi,Ki) that connects the etheric body within the physical body. (Disease is considered to be set up in the etheric body which then in turn manifests into the physical)
The physical body of a person is sustained by food and water intake and is distributed around the system by the blood stream and by oxygen intake of the lungs. The Greater self or being of a person is sustained by energy drawn into the energy centres or Chakras. This energy is then distributed around the physical body by a network, again unseen which may closely compare with Meridians used by accupuncture practitioners, the fine network of subtle channels are called Nadis.
Reiki Masters and Practitioners are able to help balances these centres (Chakras) to promote health and well being. It is a very subtle Therapy which can be hands on of for people who do not like to be touched can be performed by holding the hands above the body.