Gastritis literally means inflammation of the stomach lining. This is my understanding: (please - anyone - correct me if I'm wrong) You can have gastritis with or without GERD and vice versa. However, they often go hand in hand because gastritis can be caused by chronic reflux (as well as infection or other trauma) and GERD can be caused by gastritis (the stomach lining is inflammed - the esophageal sphincter gets "lazy" and opens because of the inflammed lining and acid reflux occurs).
I was having such horrible chest pain and abdominal pain at the same time, my doctor put me on medication for upper GI, then lower GI, nothing seemed to work and on and on and on...I got very frustrated and turned to the internet (which is where I found this website) and I learned a lot on the way! From all the reading I did on the internet about gastrointestinal disorders, this is my understanding of gastritis.