The priority field lets you assign a level of priority and urgency to each activity. Since your ToDo list is sorted by priority this lets you juggle the order in which you view and complete activities.
A two-character code denotes the priority of an activity. The first character signifies the importance or priority of the activity denoted by the letter A, B, or C. The second character signifies the urgency of the activity, and is denoted by a number 1 through 5 (9 for on hold).