Vertical line function is a bit of a misnomer, because it's dealing more with the geometric nature of a vertical line than with a mathematical function. Nevertheless, this concept is often useful in mathematical discussions and here's how it works:Understanding: Firstly, you should understand what a vertical line is. It is a line that runs straight up and down, parallel to the y-axis of a coordinate plane. Its slope is undefined.Equation: Generally, the equation of a vertical line on a graph is given as x = c where c is a constant. This is because for all points along that line, the x-coordinate remains the same.No Function Rule: A vertical line does not pass the vertical line test, and therefore does not represent a function. The vertical line test states that if a vertical line can intersect a graph at more than one point, then the graph does not represent a function.Uniqueness: In a vertical line, one x-value corresponds to many y-values. This, as per the definition of a function which states that every input must have exactly one unique output, is why a vertical line is not considered a function.Example: To understand better, let's take an example. If you consider the line x=3, it's a vertical line passing through the point (3, 0). But it doesn't correspond to a function because for x=3, there are many different y-values (i.e., every point on the line x=3 has the x-coordinate 3, while y can take any real value).I hope this helps in understanding why a vertical line is not considered a function and clarifies the characteristics of a vertical line in coordinate geometry.