Okay, imagine you have a toy box filled with lots of different toys, like blocks, dolls, and cars. These toys are called "pieces". Now imagine you have a game that you like to play, like chess. The pieces you use in chess are very specific and have rules about how they can move.
Now, imagine that instead of just having chess pieces, you have a whole bunch of different kinds of pieces that can be used in different games. These pieces also have rules about how they can move and what they can do. This big collection of pieces and their rules is called a "ludeme".
So, a ludeme is just a fancy name for a collection of game pieces and their rules that can be used to play different games. It's like having a big box of toys that you can use to play lots of different games, but each game has its own specific set of rules for how to use the pieces.