The cervical mucus plug, also known as the cervical plug or simply the mucus plug, is a vital part of the reproductive system in female mammals. It forms in the cervix during pregnancy to protect the growing fetus from harmful bacteria and pathogens. While there are no exact synonyms for the term, it is sometimes referred to as the cervical secretion or cervix mucus barrier. Other related terms include cervical discharge, cervical mucus barrier, cervical mucous plug, and cervical mucus seal. These terms all refer to the sticky, gelatinous substance that fills the cervical canal and acts as a barrier to protect the fetus from infections and other foreign matter.