A baker's dozen is 13. Apparently, in years gone by, the punishments were harsh for bakers whose weights and measures were in any way disadvantageous to the buying public. To avoid such a fate, the bakers would give 13 items to someone who ordered a dozen, ensuring the total weight was well over the advertised amount.
Thus, I can congratulate Guy Sapirstein, my regular Sunday morning ride partner, who today completed a baker's century - 110 miles - from Boston (well, Revere) to Portland (Maine). The weather was pretty miserable for much of the day ("only the first 102 miles") with driving rain and wind. However this was Guy's first century ride (one more than me), and even with a spill on slick roads at 20 mph early in the day, he completed it at a pace of around 15 mph in good spirits.
Guy rode in the "Ride to Cure Parkinsons" and you can read more about it and sponsor him here.