Metabolism in health means the chemical processes that occurs within a living organism in order to maintain life.
A persons metabolism is the process of your body converting what you eat and drink into energy to allow you to sustain life and move around and do things.
Your body uses the food for energy and drinks for energy as well just like gasoline is the fuel for vehicles your food and drinks are fuel for your body.
Your metabolism then converts that food and drinks into energy just like a vehicles throttle body converts the gasoline into energy for the vehicle along with the spark plugs, ignition etc.
Your metabolism is very important to converting the food and drinks into the needed energy for our bodies.
Also during the metabolism complex biochemical process, calories in food and beverages are combined with oxygen to release the energy your body needs to function properly.