Recently i saw the following article on wikipedia to see whether a graph is a graph of a function or not.
It states that To use the vertical line test,"draw a line parallel to the y-axis for any chosen value of x. If the vertical line you drew intersects the graph more than once for any value of x then the graph is not the graph of a function. If, alternatively, a vertical line intersects the graph no more than once, no matter where the vertical line is placed, then the graph is the graph of a function."
So in case of a parabola with $y^2=4ax$ a line $\parallel$ to the $y-axis$ will cut it into two points. So $y^2=4ax$ is not a function?
Wikipedia writes the same: "As an example, a sideways parabola (one whose directrix is a vertical line) is not the graph of a function because some vertical lines will intersect the parabola twice."
Am I having any confusion? Please help.