Health is the state of the absence of illnesses or injuries, as well as the state of physical, mental, and social well-being.
Wellness is the process of maintaining the healthy state of the organism based on individual lifestyle choices.
D.L. Stoewen (2015). Health and wellness. Can Vet J. 56(9), pp. 983-984. PMID: 26345732; PMCID: PMC4535518.