I remembered our birth class teacher talking about this, so I googled it and found it under a health reports "first signs of labor." I haven't had any contractions today, so it could still be awhile. It's just neat that these things are really happening.
"Bloody show: Loss of mucus plug
During pregnancy, a thick plug of mucus blocks the cervical opening to prevent bacteria from entering the uterus. When your cervix begins to thin and open, this plug may be discharged. You may notice stringy mucus or a thick discharge. It's typically brown and sometimes tinged with blood.
Losing the mucus plug is a sign that labor may begin soon, but it's not a guarantee. Labor may still be a week or more away."