What does it mean to be physically and mentally fit?
Do you have the ability to do the activities you love? With no second guessing, fear of getting injured, missing out on playing with the kids.
Check out this definition from 70 years ago. Not much has changed since that time. Though constantly living on social media is unlikely to help the 'social well-being' aspect. Pretty sure the author didn't have a cell phone, but engaged with real people once in a while.
The World Health Organization (WHO) defined health in its constitution of 1948 as "a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity".