What is the rule of 75 in cycling?

Excuse me, could you please clarify for me the concept of the "rule of 75" in cycling? I've heard it mentioned before but I'm not entirely sure how it's applied or what it signifies. Is it a performance benchmark for cyclists, or perhaps a strategy employed during races? I'd appreciate if you could elaborate on its significance and how it might be used in the sport. Thank you in advance for your explanation.