Reiki is the awareness that an unseen energy flows through all living things & directly affects the quality of a person's health has been part of the wisdom of many cultures since ancient times.  This life energy goes by many names:  qi in China, ki in Japan, & prana in India.  The ancient Hawaiians called it ti or ki.  It has also been called orgone energy & elan vital, & science refers to it as biofield energy.  

When your life energy is low, it is more difficult to deal with stress; you may not sleep well, & you're more susceptible to illness.  When your life energy is strong, you feel strong, can more easily deal with stress, & are less likely to get sick.  Reiki is a technique that increases a person's supply of life energy.