(biology) a hypothetical force (not physical or chemical) once thought by Henri Bergson to cause the evolution and development of organisms
"Henri Bergson proposed that vitality is a distinct, non-physical force driving the evolution of living organisms."
The capacity to live and develop.
"The gardener added compost to restore vitality to the exhausted soil, allowing new plants to sprout and grow."
In plain English: Vitality is the energy and liveliness that makes you feel strong, healthy, and full of life.
"The fresh air and sunshine restored her vitality after the long winter."
The word vitality comes from the Middle French term vitalité, which was borrowed from the Latin vitalitas meaning "vital force" or "life." It entered English as a noun form of the adjective vital to describe the quality of being strong and energetic.