Decaffeination is a process to remove caffeine from things like coffee or tea. Caffeine is a chemical in these things that makes them taste bitter and can make us feel jittery or restless if we have too much. So some people choose to have decaffeinated coffee or tea instead, which means they won't get that jittery feeling.
There are a few different ways to decaffeinate things, but one common way is called the "Swiss Water method." In this method, the coffee or tea beans are soaked in water to create a "coffee soup." This helps to dissolve the caffeine from the beans. But they don't want to lose all the other flavors and chemicals that make coffee or tea taste good, so they use a special filter to remove the caffeine molecules without removing anything else.
Another way to decaffeinate coffee is to use a chemical solvent. This sounds scary, but it's actually safe and FDA-approved. The solvent is usually either methylene chloride or ethyl acetate. These chemicals are good at dissolving caffeine, but (like the Swiss Water method) they are careful to only remove that one chemical and not any of the other flavor or aroma molecules. After the solvent removes the caffeine, it is washed away and the beans are dried.
So that's decaffeination! It's a process to remove caffeine from coffee or tea so we can enjoy the taste without feeling jittery. But remember, always drink decaf in moderation and don't drink too much caffeinated coffee or tea either!