In backgammon, Performance Rating (PR) is a statistic that measures a player's skill level. It's calculated by comparing a player's average move against the move deemed best by a backgammon analysis program. Essentially, it quantifies how much a player loses in equity (or "milipoints") per move compared to the ideal move. 

Here's a more detailed explanation:

• What is Performance Rating (PR)?
  PR is a way to assess how well a player is making decisions in backgammon, compared to the optimal moves a powerful computer program would choose. 
  
  
• How is it calculated?
  A player's PR is determined by comparing their average move to the best possible move in a given backgammon position. 
  
  
• What does a lower PR mean?
  A lower PR indicates that a player is making moves closer to the ideal move, and is therefore considered a more skilled player. 
  
  
• How is it used?
  PR is often used to rank players, award titles (like Super Grand Master, Master, Intermediate or even a Beginner), and even to determine seeding in tournaments. 
  
  
• Limitations of PR:
  PR primarily focuses on the quality of individual moves and doesn't fully account for factors like exploitative play or the influence of luck. 
  
  

In essence, PR is a tool for assessing backgammon skill based on how closely a player's decisions align with the ideal decisions a top-tier backgammon analysis program would make.