Position
The numbers indicate the position the horse finished in its most recent races. So 1 means first, while 0 normally indicates a placing out of the first three or four.
The dash (-) in between figures separates this season from last. The slash (/) separates this season from the season before for a horse which did not race last season.
P means the horse was pulled up and did not finish. R shows the horse refused to race. In jump racing, F is for a faller, while U says the horse unseated its rider.