Mixed boundary condition

Okay, so let's say you're playing a game of tag with your friends. You have a rule that you can't leave the playground, but you're allowed to touch the fence and the tree that are on the edge of the playground.

This is kind of like a mixed boundary condition in math. It means that on one part of a boundary (like the fence), you have one type of condition (you can touch it). But on another part of the boundary (like the rest of the playground), you have a different type of condition (you can't leave it).

In math, this can come up when you're trying to solve equations or problems. You might have some parts of a boundary where you know the answer (like the fence), but other parts where you don't (like the rest of the playground). So you have to mix different types of conditions to solve the problem as a whole.