A Moore graph is a special kind of graph where every vertex has the same number of neighbors or "friends". Imagine you're playing a game where you have to connect dots with lines or "edges". In a Moore graph, each dot would have the same number of lines connecting it to other dots.
For example, if you were playing with 5 dots, and each dot had 2 lines connecting it to other dots, then you would have a Moore graph of 5 vertices and degree 2.
Scientists like Moore graphs because they have special properties. For example, they're the most connected graphs possible for a given number of vertices and degree. They're also really good at packing things together tightly, like in the design of computer chips or networks.
So, think of a Moore graph as a special kind of game where every dot has the same number of lines connecting it to other dots, and scientists like them because they have some neat properties that make them useful for solving tricky problems.