TP + FN means true positives plus false negatives, that is the number of deseased people. P should be the number of people that gives positive in the test, since TP means true positive in that sense.

Also TP + FN = Prevalence of the desease, but using P for prevalence and for positive creates a lot of confusion in a wikipedia page to explain a concept.

My plea is that I don't want people to get confused. On top of it there is a warning on that page of wikipedia: This article may be too technical for most readers to understand. I couldn't understand why they used that notation. So I ask to delete that page because is going to confuse people.