What exactly does it mean when you have a brown discharge after having sex?

Old blood: Brown discharge is old blood. Typically that blood is coming from inside the uterus, but it could be coming from the cervix as well. Likely sex caused a sloughing off of the brown discharge, again, either from the uterus or the cervix. If it only happens occasionally not to worry. If you are having it with every act of intercrouse, or bright red blood after intercourse, then see your doctor.