Can you explain the differences between severity and priority?

"The terms severity and priority typically apply to time management. I use them to determine which problems I'm going to work on first. Severity defines how difficult a problem will be to resolve. Priority defines how important the issue is to the organization and the impact of fixing it. A good illustration of this is to create a diagram with four quadrants. On the Y-axis is priority and on the X-axis is severity. My focus is on the upper right quadrant, which contains high priority in high severity issues. I avoid the lower left quadrant in which both of these are low. After resolving high priority and high severity issues, I then address a high priority before resolving high severity."