DNP = Did not place. Some officials will announce that they will only place through "x" spots/positions. DNF = Did not finish. This means you pulled yourself out of the race or you were pulled.
Most officials will pull and place after about 1/2 of the race. In really hectic cat 5 short crits.....they're going to pull and probably only place the top 20 or so.
In general this is only used for entry level races.....both mean you need to HTFU. I should know. I have DNF'd plenty. I only DNP'd about 2 or 3 times. Almost all were Superweek where they are too lazy to place the whole finishing field.