In this function, y is the dependent variable and x is the independent variable. Variable used in an experiment or modelling can be divided into three types:  dependent variable ,  independent variable , or other.
About 70% of men have an eye dominance that matches their handedness. BUT, 30% do not. Most right handers have a dominant right eye and the bulk of southpaws a dominant left. These are the people who are well advised to shoot both eyes open (assuming that they are shooting from their strong shoulder).
Shooters using the red dot scopes should try to use their dominant eye to view the dot. I see this dot so naturally with my left eye (even though I'm right-handed) that I don't need to occlude my right non-dominant eye. My brain would suppress the scope image of my right eye.