Final answer:
The equation x = -6 represents a Vertical Line on a graph, as it denotes a constant x value with no dependence on the y value, differing from typical slope-intercept form linear equations.
Step-by-step explanation:
The best description for the linear equation x = -6 is a Vertical Line. This is because the equation specifies a single value for x, regardless of the value of y, which means all points on the graph of this equation will have an x-coordinate of -6. There is no slope-intercept form (y = a + bx) applicable because 'x' does not depend on 'y' in this equation; hence, it does not depict the behavior of a typical linear equation with a slope and y-intercept.