Gastritis is the inflammation of the stomach lining, which can be acute or chronic, often caused by factors like H. pylori infection, NSAID use, and excessive alcohol consumption. Common symptoms include abdominal pain, nausea, and bloating, while severe cases can lead to complications such as gastric ulcers and cancer. Diagnosis typically involves history taking, endoscopy, and various tests, while management includes medications, dietary modifications, and, in rare cases, surgery.