It means whatever value of x you take , the corresponding value of y will always be -4 .
Mathematically if f ( x ) is a function .
f (x) = y = -4 .
so f ( 0 ) = -4. for x = 0 ; therefore we get point 0,-4
f ( 1 ) = -4 for x = 1
f ( 27) = -4 for x = 27 ; therefore 27,-4 in also a point satisfying the equation .
Thus for any point with whatever x - cordinate, the value of y co ordinated will be -4 only .
hence the answer is :y=-4