Gastric cancer refers to a type of cancer that originates in the stomach. It is also known as gastrointestinal cancer or stomach cancer, and it occurs when cells in the lining of the stomach grow out of control and form a tumor. This can be due to genetic mutations or other factors such as diet, lifestyle, and environmental exposures. Gastric cancer is classified into different types based on the type of cell where it originates - such as adenocarcinoma (the most common type), gastrointestinal stromal tumor, or lymphoma. It can be treated through surgery, chemotherapy, radiation therapy, or targeted therapy depending on the stage and severity of the cancer.