Short - tables where the max buy-in is a short stack, usually 50 bb max. PRR = Progressive rake race. It means playing at those tables earn points towards weekly leaderboards. Pl/Fl = (percentage of) players seeing the flop. Usually used to indicate how tight or loose the table is playing on average.
The lower the SPR, the broader range of hands you should be willing to stack-off with, for example, top pair. The deeper and larger the SPR, the value of what becomes a good hand (that should be fist-bumping to stack-off/get-it-in) increases to hand values like sets, straights, and flushes.