Answer: Undefined slope.
Explanation:
Zero slopes are slopes that don’t increase on the Y axis at all, therefore this isn’t a zero slope. Undefined slopes are like elevators, they can only move straight up and straight down. It got its name “undefined” from the fact that it is impossible to divide by zero.
Remember:
Slopes that only have a run are zero slopes
Slopes that only have a rise are undefined slopes
Anything else is either a positive or a negative slope.