Okay kiddo, you know how when we make tea, we usually just put a tea bag in hot water and let it sit for a few minutes? Well, fermented tea is a little bit different.
Fermented tea is made by taking tea leaves and adding a special kind of bacteria and yeast to them. This bacteria and yeast mix with the tea and create something called a "tea fungus" which floats on top of the tea.
This tea fungus eats the sugars in the tea leaves and changes them into different things, kind of like how you change Play-Doh into different shapes. The fungus creates new flavors and makes the tea taste a little bit sour or tangy.
Sometimes people like to add some sugar or fruit to their fermented tea to make it taste even better. Fermented tea is also called "kombucha" and some people think it has health benefits too.
So, basically, fermented tea is tea that has been changed by adding special bacteria and yeast, and it tastes a little bit sour or tangy.