Firstly, it usually refers to the "arithmetic mean", known as "the average".
The average is when you add all of the numbers together, then divide by how many numbers there are.
However, there are other types of mathematical means, including the geometric mean, harmonic mean, and the mean of continuous random variables (known by statisticians as the "expected value").
Inspiration is not a mathematical term. It, therefore, means what it does in normal usage.
The Same Position
It means the amount.
It means the sum of several monomials.
It means out of all the numbers which is the middle