What does “each point of a line maps to itself” mean? I don’t understand it what it means for it to map to itself.

Answer:
Step-by-step explanation:
For example if you have a function f(x) = x - 1, then x = 1 is a zero of this function because using it as x gives 1 - 1 = 0. The Riemann Zeta function has some zeros that are easy to find which are of little interest but there are some other ones that are harder to find which is why the are called non-trivial.