ADP Average Draft Position	Close
Average Draft Position (ADP) is the average overall draft slot that has been used to draft each player in real or mock fantasy drafts.  ADP reports have been available to fantasy owners for years from sites like antsports.  Draft Planner displays ADP data collected from at least three web sites and averages them together.  The raw ADP data showing which site provided each value and when can be viewed here.
The Math
ADP is the simplest approach for determining player value.  If Player A has been drafted 1st in five drafts and 4th in five drafts, he has an ADP of 2.5 ((1*5 + 4*5)/10 = 2.5).  Note that the best possible draft slot is 1 and not 0.  The enhancement brought by Draft Planner is that the ADP data is averaged from several sites.  This weeds out data problems (each player must be reported by at least 3 sources), and helps combine the different types of leagues popular at each of the league web sites.
Positives
Arithmetic is very simple A player's true value on draft day is defined by where he is drafted and not where he is listed on someone's cheat sheet
Negatives
Does not consider league scoring rules Can become a self-fulfilling prophesy (If everyone used ADP to help determine who they draft, players may be reinforced simply by tradition.)
During the draft
Unlike most other player value lists, ADP does give you some idea about the order in which players should be drafted.  Although league roster sizes can throw the ADP values off, it can definitely be used during a draft to determine if a player justifies his draft pick.  The goal is to draft a player whose ADP value is in-line with the other players drafted near the pick.  Draft a player with a higher ADP value than those around him, and you will have overpaid.  A player picked with a lower ADP value than those around him is considered a bargain. The most effective use of ADP is to combine it with drafting tendencies and a real-time analysis of what is going on in the draft.  Average Draft Position (ADP) is helpful for determining where players are actually being drafted, but determining how much more or less a player is worth than their pre-draft value is dependent upon how many things can be considered in the time it takes to make a draft pick.  A great drafter will be able to consider factors such as everyone else's roster status, their estimation of player values, remaining strength at each position, bye week implications, back-up needs, etc.  Computer programs such as Draft Predictor are often employed to analyze this data and combine it with a list of player values to suggest and even predict draft selections.  Draft Predictor uses ADP in two ways: It is shown along-side the player values in the cheat sheet.  If you are using a PAVT, RLV, or custom cheat sheet, the ADP data is shown in its own column so that you can run a quick check to make sure that you are not over-paying for the player. The ADP values can also be used as the actual player values within the cheat sheet.  This can assist with the prediction accuracy of Draft Predictor since it causes other owners to perform an "average" draft, but it also provides a good baseline cheat sheet.
Acknowledgements
ADP has been around for as long as there have been fantasy football leagues.  For more information on how it has been used and how it can be leveraged, see FantasyFootball.com Fantasy University Series: ADP.