A mucus plug is a plug of mucus that is there to protect the baby from the outside world while it develops in your body.
When the mucus plug comes out it means that pregnancy is about to begin and it could happen soon after as in a few hours or the pregnancy might not happen for a few more days.
It means that the baby has developed and is about ready to be born and leave your body.
When a mucus plug comes out it'll either be blood tinged or streaked with old blood that is brownish in color.
Just know that soon you might be going into labor if your mucus plug does come out.