I googled it for you as I was just as curious and this is what I found at:
http://www.medhelp.org/posts/Pregnancy-Nov-09-Babies/34-weeks-pregnant-Mucus-Plug/show/1074604
As you near the end of your pregnancy, your cervix will begin to thin out and dilate. As it changes, you may lose your mucus plug and find a gooey deposit in your underwear or on the toilet tissue after wiping. It is not uncommon for this mucus to be mixed with brown, pink, or red streaks of blood from the changes occurring within your cervix. Some women may lose the plug at 36 weeks' gestation, while many others may not lose it until labor has begun. Sometimes moms-to-be may not even notice that they are losing their mucus plug because it happens gradually, over several weeks, and they've already grown accustomed to varying but increased amounts of the vaginal discharge that often accompanies a normal pregnancy. If you are earlier than 36 weeks' pregnant when you see blood-tinged mucus, or if you have any vaginal bleeding beyond the first trimester, you should call your practitioner.
Is labor soon to follow?
Rumors seem to abound when it comes to what it means to lose your mucus plug. While there's hardly a pregnant woman out there who doesn't wonder when exactly she will go into labor, the appearance of the mucus plug does not answer this question with any certainty. That said, loss of the mucus plug is often the first sign that labor is approaching. Before you make a mad dash to Labor and Delivery, however, remind yourself that many women do not go into labor for a week or two after this event. In fact, if you are full term--which almost by definition means that you'll be welcoming your new baby within the next few weeks--there is usually no need to even make an after-hours call to your practitioner.
Whatever the case may be, be kind to yourself during this time. Sit back, try to relax, and let nature take its course. Make sure to get plenty of rest because you will need it after labor begins. You may be on your way to helping along a miracle any day now.