The fourth stomach is a term used to describe the digestive organ found in ruminant mammals. This stomach is also known as the abomasum. However, there are other synonyms for the fourth stomach that are used in different regions and contexts. For example, it is sometimes called the rennet stomach due to its role in producing rennet, a key ingredient in cheese-making. Another term for the fourth stomach is the true stomach, distinguishing it from the three other stomachs found in ruminants. Additionally, the fourth stomach can be referred to as the Gastrointestinal (GI) tract or digestive system, as it is an essential part of the overall process of digestion in these animals.