The root for the word Holism goes back to Early Greek, meaning that properties of a system cannot be determined or explained by the sum of its components alone. First coined as a word by Jan Smuts in about 1922, and used to define "The tendency in nature to form wholes that are greater than the sum of the parts through creative evolution." Often times described as the opposite of reductionism, holism may also be contrasted with atomism.
Holism due to its nature is an extremely controversial issue, and many philosophers and scientists beleive many of the claims behind holism to be false. With that in mind though, their are several ideas that have come about from holism that are considered main stream in contemporary philosophy.
In todays ever changing society we are most familiar with holism in the form of "holistic healing". The holistic method of healing is to recognize that the emotional, mental, physical and spiritual elements of each person make up a system, and then tries to treat the person, with this in mind, with emphasis on the cause of the problem and the symptoms. Because of its roots, and the emphasis on the body as a whole, holism rarely uses pharmaceutical drugs,etc. and focuses primarily on traditional medicine such as : Reflexology, Indian Head Massage, Reiki and Acupuncture.
Holism is an extremely interesting topic, and if it is something that you are interested in I would recommend a visit to your local library, or a quick search on the internet for a wealth of information, so that you can become more informed.