Answer: Horizontal
Step-by-step explanation: The equation y = -2 can be thought of as y = 0x - 2. So our line has a slope of 0 and a y-intercept of -2.
To graph it, we start with the y-intercept, down 2 units on the y-axis. Now, if the slope of a line is 0, then the line must be flat or horizontal.
So we just draw a horizontal line through the y-intercept of -2.
In fact, when the equation of any line reads y = a number, it's graph will always be a horizontal line. For example, y = 3, y = -10, y = -8 and so on.
Image provided below.