This table shows the % chance you have of rolling each legendary item in the game once you find a legendary item in that slot. In other words the Drop % number means that for every 100 legendary items you loot in a particular slot, approximately X% of the corresponding item will drop. (X% being the number in column K corresponding to the item in Column C)
For example, if you kill a monster and the game determines that it should be a legendary belt, you will have a ~10% chance to receive 8 common legendary belts, a ~5% chance to receive 4 rare legendary belts, and a ~1% chance to receive “The Witching Hour” belt. To simplify the sheet I used the max drop value for each row rather than the actual drop rate of each class. The exact percentages for each slot will change depending on which class you are playing and the total pool of legendary items that your class can roll in that particular slot.
Also, these are only the drop rates for smart loot rolls. 15% of drops are not smart loot drops, which is why you will occasionally receive a legendary item which is for a different class or has a different primary stat.