What is the 85 per day rule in Spain?

Excuse me, I'm quite curious about the 85 per day rule that I've heard mentioned in Spain. Could you possibly explain what this rule actually entails? Is it some sort of financial regulation or a labor law? I'm trying to understand its implications and how it might affect individuals or businesses operating in Spain. Could you please elaborate on the specifics of this rule, including any exceptions or conditions that might apply? Thank you for your time and assistance in clarifying this matter for me.