It is a science of maintaining positive health and eliminating disease state.
Sushruta has defined health as:
// Samadoshah samagnishcha samadhatu-malakriyah /
Prasanna-atmendriyamanah swastha ityabhidiyate //
A person is healthy when he possesses in normal state the doshas (biological humours) agni (metabolic fire) and dhatus (body tissues) and malas (waste products)in his body and his soul, mind and organs of cognition and conation are in perfect state of co-ordination and his mental disposition is in happy and cheerful state.