The slope is undefined.
When we use the formula to find slope, (-6 - -5 / -3 - -3) we would get -1/0 and numbers with a denominator of zero are undefined. We could also figure this out by drawing it out on graph paper, and we would see that a line that goes through (-3,-5) and (-3,-6) would go up and down, which is a sign that the line has an undefined slope.