I was reading through the expository paper https://math.berkeley.edu/~dcorwin/files/etale.pdf In chapter 1 section 1.1.2 the statement says
We have $H_1 ⊆ H_2$ iff $Y_1$ dominates $Y_2$
It basically says given two covers $Y_1$ and $Y_2$ of a space X with $Y_1$ "dominating" $Y_2$, the fundamental group corresponding to $Y_1$( say $H_1$) and $Y_2$( say $H_2$) follows that $H_1 \subseteq H_2$
Here i clearly do not understand what does one mean by covering space $Y_1$ dominates another covering space $Y_2$ . can someone please explain what it is and hoe this inclusion is justified.
Thank you