विश्व स्वास्थ्य संगठन (W.H.O.) ने सन् 1948 में स्वास्थ्य या आरोग्य की निम्नलिखित परिभाषा दी गई है।

1) दैहिक, मानसिक और सामाजिक रूप से पूर्णतः स्वस्थ होना ही स्वास्थ्य है।

Health has a variety of definitions, which have been used for different purposes over time. Health can be promoted by encouraging healthful activities, such as regular physical exercise and adequate sleep, and by reducing or avoiding unhealthful activities or situations, such as smoking or excessive stress. Some factors affecting health are due to individual choices, such as whether to engage in a high-risk behavior, while others are due to structural causes, such as whether the society is arranged in a way that makes it easier or harder for people to get necessary healthcare services. Still, other factors are beyond both individual and group choices, such as genetic disorders.