Question

why is horizontal power sharing also known as a system if checks and balances?

Answer 1

This is because each level is placed at the same level which can exercise powers independent of the other! But the legislature can check the the other 2 levels so that they do not exercise unlimited powers

Answer 2

this is coz these systems share equal powers. like legislative have the power to make laws, executive have the power to enforce these and judiciary have the power to implement those.