Chris Rayburn has "devised a Value metric for comparing player values in DFS that 4for4 will be shifting to [in 2017]. The metric, which we will refer to simply as "Value," uses multi-year historical data to determine a player's scoring expectation based on two things: (1) salary and (2) position."
The above text is copied from the article explaining this new VALUE metric, and is what the line-up generators are referring to in the "VAL" column.