It’s a familiar concept that is used for strategic elements in Pocket Mortys. Each Morty has a designation of Rock, Paper, or Scissors, and the familiar rules apply. For example, a rock based Morty will do better against a scissor Morty, but is vulnerable to a paper Morty. You need to use this knowledge to try to have the match up in your favor, or at least a draw to have a Rock Morty facing another Rock Morty.
You can carry a team of up to five Mortys, and you will want to balance it out, so you have a rock, paper, and scissors Morty at your disposal. The game requires you to keep the standard Morty, and then you can have one of the other three designations on your side. In a given battle, you can switch out your Mortys to try to gain the RPS advantage, but that will cost you a turn or two, so be careful of switching too often.