what does y=x

does anyone know what y=x is

Equation of a line that divides the first and third quadrants in half

Being 6 th grade it could be the beginning of function

If x = 1 , then y = 1
If x= 2 , then y = 2

Y=X ???

Well, if y=x, you replace the y with any number, but that number is also used in x.