Something that completes or enhances something else when added to it.
Walking lunges are supplementation for lower body muscle endurance.
Books are supplementation for humans looking to improve mental capacity and creativity.
Vitamins, herbs, minerals are supplementation to food for humans for changes required in health and fitness.
Over the past 20 years I have discussed food supplementation less and less in our CCP Nutrition Course. The course itself is designed to teach fitness coaches the basics on food consultations for their clients.