It is common practice to taper one's training during the final days/weeks before a race. The length of the taper corresponds to the length of the race, generally. There are different philosophies and explanations for the taper, and while some suggest during the taper the runner should cut back on speed work, so the muscles are totally healed up and strong on race day, the prevailing approach today appears to be to decrease overall mileage, while maintaining normal intensity in short and middle-distance runs at first, then closer to the race cutting back on intensity as well. This latter approach appears to make sense because aerobic capacity can be effectively maintained on two-thirds of ones normal aerobic mileage, while anaerobic mechanisms seem to require consistent higher-intensity effort to maintain.
In other words, we gain and lose aerobic endurance (ability to run long periods at a slow/moderate pace) slowly, while we gain and lose stamina (ability to maintain high-intensity effort) more quickly. The idea of this kind of taper is to optimize the mixture of aerobic and anaerobic effort to maintain the endurance and stamina we have already built through our normal training regimen, not to add to it. We want our muscles to be fully healed, our muscle's metabolic systems to be tuned to what we are about to ask of it, and to be well-rested. That latter part amounts to insurance that our bodies have fully replenished their energy stores (glycogen in liver and muscle tissues), so it also requires sound nutritional planning.
So, what does a taper look like? With some variations, A taper for a 5K race may be little more than resting or only light/short runs for two days before the race and avoiding speed work during the 5 days before the race. For a 10K, The taper period might be fairly similar to that for the 5K, but may go for 7-10 days before the race, depending on a runner's normal training mileage. For a half marathon, people seem to taper for 7-14 days, during which total mileage is decreased to some extent, while speed work is maintained until the final 5 days before the race, which the taper begins to look the same as for the shorter races. For Marathons, the taper is similar overall, but may be more progressive and last for 14-21 days, depending on the runner.
The specific types and durations of runs that runners do during their tapers will depend on the individual and should match their normal training loads, which also depends to some extent on what a runner's overall goals have been in training and for the race. Was the goal simply to finish? To PR? To win? The answers to these questions usually determine the volume of endurance vs. stamina and speed training a runner does in everyday training.
I relied on my previous research on tapering for races in a variety of sources, conversations with other runners, and responses of several runners in Dailymile for the information I've summarized above, and this also made it clear just how much personal preference and experience come into play during the taper. For example, in the rest period leading to the race, some people do nothing the last two days. Some people do a 20 minute run with a couple of 1-min race pace pickups, the day before the race. Some people do an easy 20 minute run on both days at recovery pace with no pickups. Earlier in the final week of taper people either include a shortened interval workout that doesn't leave them fatigued, a short race pace run with a good warmup and cooldown, or simply a 20-30 min. tempo or steady-state run. Earlier in the taper, the variation is as much about what training plans (if any) are being followed leading into the taper as to personal preference, goals, etc...
Overall, I'm impressed by the number of different tactics (specific things) used during the taper, while the overarching strategy (general approach) today seems to be consistent among most runners. It seems that we are either all listening to the same experts these days, and our collective experience has taught us something (I hope) about the best way to prepare in the days/weeks before a race. I'm quite sure I've probably missed some things that people do here, including voodoo rituals involving chicken blood, bonfires and naked dancing, and I'm left out the nutritional considerations as well. :)