Ayurveda or Ayurvedic medicine is an ancient system of health care that is native to the Indian subcontinent. It is presently in daily use by millions of people in India, Nepal, Sri Lanka and indirectly through it being the major influence on Unani, Chinese and Tibetan Medicine. The word "Ayurveda" is a tatpurusha compound of the word ayus meaning "life" or "life principle", and the word veda, which refers to a system of "knowledge". Thus "Ayurveda" roughly translates as the "knowledge of life". According to Charaka Samhita, "life" itself is defined as the "combination of the body, sense organs, mind and soul, the factor responsible for preventing decay and death, which sustains the body over time, and guides the processes of rebirth". According to this perspective, Ayurveda is concerned with measures to protect "ayus", which includes healthy living along with therapeutic measures that relate to physical, mental, social and spiritual harmony. Ayurveda is also one among the few traditional systems of medicine to contain a sophisticated system of surgery (which is referred to as "salya-chikitsa").