Imagine you have a bunch of shapes - circles, squares, triangles, and so on - and you want to arrange them in a certain way. However, you can only move them around by rotating or reflecting them. Now, some of these shapes might be exactly the same, even if they look a little bit different. For example, a square with one side pointing up and one to the side is the same as a square with one side pointing to the right and one down.
The congruence lattice problem is a math problem that asks: when you have a bunch of shapes that can be rearranged by rotating or reflecting them, and some of them are actually the same, how can you group them together in the best way?
For example, say you have ten squares of the same size, but they're arranged in different directions. You might group them into three different categories: the four with sides pointing up, the four with sides pointing to the right, and the two that are diagonal. You can then rotate or reflect any square within that group and it will still be the same.
The problem becomes more difficult when you have more complex shapes, like pentagons or hexagons. Sometimes you might think two shapes are the same, but you can't quite prove it. Other times, you might group some shapes together, but later on you realize you made a mistake and need to rearrange them again.
Overall, the congruence lattice problem asks how to organize a set of shapes based on their similarities and differences, taking into account the various ways you can transform them through rotation and reflection.