The term "bag of waters" is often used to describe the amniotic sac, which is a fluid-filled sac that surrounds the developing fetus during pregnancy. There are several synonyms that can be used to describe the same thing, such as "amniotic membrane", "amniotic sac", or simply "water bag". Another common term is "the membranes", which refers to the thin layers of tissue that make up the amniotic sac. In medical settings, healthcare providers may use more technical terms like "chorioamnion", "amnion", or "allantois". These synonyms can be used interchangeably to describe the same structure and help to better understand the pregnancy and childbirth process.