To put into perspective how close a relation this mystery 5% man is to me, look at my closest genetic relations in the database.
The P stands for Paternal Match and the M stands for Maternal Match.
D. W. is my known first cousin, twice removed. The displayed relation of 2nd cousin is a prediction. Second cousins (children of first cousins) should share about 3.125% DNA. D. W. is my grandfather's first cousin, so the same spacing exists between us as second cousins. [For DNA purposes, D. W. is better than a second cousin because he represents the DNA from two generations ago at my grandfather's generation.]
This mystery 5% cousin shares slightly more DNA with me than D. W. does! That is how close a relation he is to my mother's family and why I really wish he would come forward.