It's related to implied odds. It's the ratio of your stack size (or your effective stack size if you have everyone else covered) to the size of the pot on the flop. Basically you would ideally like an SPR >= 20 with a drawing hand (small pocket pairs, small suited connectors, baby suited Aces, etc), and an SPR < 10 if your hand is most likely going to flop top pair (e.g. a big pocket pair or a big AX hand). You generally want to adjust your pre-flop betting to avoid SPRs between 10 and 20. It has to do with how many bets its going to take to get all-in by (or before) the river, assuming you want to play for stacks (or at least make your opponents think you do). With a premium hand, you want to charge your opponent as much as possible to draw against you, so you want the SPR low, and deny your opponents sufficient implied odds to chase past the flop (e.g. either shove the flop or make a big enough bet that it's obvious you'll shove the turn). If you can't do that (e.g. if stacks are really deep), then you want to play small-ball.
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i don't think so.....:-\
At least, that's the general idea.