Supersaturation is like having too many toys in your toy box. You want to put more toys in, but there's no more room for them.
In science, we use the term "supersaturation" to describe a situation where we have a lot of a substance (like sugar, salt, or any other thing that can dissolve in water) in a liquid (like water), but there's no more room for that substance to dissolve.
Just like you can't put any more toys in your toy box when it's already full, the liquid can't hold any more of that substance when it's already supersaturated.
Supersaturation can happen when we add too much of the substance to the liquid, or when the liquid gets colder. So, if you put too much sugar in your tea, you might have supersaturated tea.