424: Point-point-slope

Challenges

1. Use four different digits (from 2-9) to create two points which determine a line with the greatest possible slope.
2. Use four different digits (from 2-9) to create two points which determine a line with the least possible slope.
3. Use four different digits (from 2-9) to create two points which determine a line with a slope as close to zero as possible.

source.

What does "greatest" slope mean?
What does "least" slope mean ... most negative?