RDI stands for Reference Daily Intake and represents the daily dietary intake level of a nutrient considered sufficient to meet the requirements of nearly all (97-98 percent) healthy individuals in each life stage and gender group. Basically the RDI replaces RDA (Recommended Daily Allowance), since the RDA was expanded in 1997 (I guess I am a little behind the game since I am just now noticing it) to become one part of a broader set of dietary guidelines called the Dietary Reference Intake, which is used by both the United States and Canada. The new guidelines include the tolerable upper intake levels (UL) to caution against excessive intake of nutrients (like vitamin D) that can be harmful in large amounts.
The RDI is used to determine the DV% (Daily Value percentage) that you see on food labels. The DV is the dietary reference value displayed on food labels, So the DV is a percentage and the RDI is total amount in milligrams or grams.