I've heard different things. what exactly is gerd?

GERD may progress: Gerd="gastroesophageal reflux disease." stuff from stomach (whether acid or not) regurgitates back into esophagus--due to inappropriate relaxation of lower esophageal sphincter, impaired esophageal function (peristalsis), inadequate saliva, gastric outlet narrowing, gastroparesis, small bowel pathology, etc. Damage to esophagus may result including ulcers, scarring, narrowing, pre-cancer(barretts).

Heartburn: Gerd is the medical term for heartburn. It stands for gastroesophageal reflux disease. It is your stomach acid refluxing or rising up into your esophagus ( food pipe) which presents as a burning sensation. If left untreated for a long period it can lead to severe irritation and inflammation of the lining of the esophagus.