5x5-10 would mean do 5 sets of 5 to 10 reps. Often when the reps are listed in this fashion, if the volume is for a large compound exercise, it means that you are meant to start at a 5x5 for your first session and then progress toward doing 5x10 by increasing volume over your subsequent sessions. As a description of volume for a single exercise, that specific parameter is pretty uncommon though. Usually if you want that much volume, you want to do something like 4x8-12, so that you are forced to start with a lower load (e.g at least an 8-RM as opposed to a 5-RM) and not have to do so many sets.
Sometimes, when the volume is for an accessory exercise, 5x5-10 might just indicate the range of volume appropriate based on the what else is going on in the routine. This is usually the case when there is a specific plan for periodization of the primary lifts, which are meant to largely determine the lifter's progression, while the accessory exercises are just meant to round out that work and be progressed on as able (either by weight or reps within that range).
Most English-speaking people seem to use sets x reps x weight or some part of that, i.e. sets x reps or reps x weight. You'll sometimes see other formats among other peoples, especially if you're reading programs derived from Eastern European material or from those taught under schools of lifting that have their roots there. These other formats usually involve switching the order of the reps and sets and sometimes reversing the whole thing. Other symbols are occasionally used to delineate the sets, reps, and weights.
Last edited by chicanerous; Sat, April 21st, 2012 at 12:14 PM..