What is the IQ of average intelligence?

I'm curious, could you elaborate on the concept of "average intelligence" and how it relates to IQ scores? Is there a specific number that defines the IQ of average intelligence, and if so, what is it? Also, is it possible for someone's IQ to fluctuate over time, or is it a fixed measure of cognitive ability? Understanding these aspects could provide valuable insights into the complex nature of intelligence and how it's measured.