Gastritis is an inflammation of the gastric mucosa classified as acute or chronic, most prevalent in older adults, particularly in heavy drinkers and smokers. Common causes include corrosive substances, NSAIDs, and certain food types, leading to symptoms such as epigastric discomfort, nausea, and potential GI bleeding. Diagnosis often requires a detailed history, endoscopic examination, and various tests, with treatments focusing on symptom management and dietary changes.