Acid reflux simply means that acid made by your stomach's cells backs up through the lower esophageal junction (where your esophagus and stomach meet). At low levels, acid reflux is a normal part of digestion and movement along the gastrointestinal tract. In normal patients, acid reflux can cause symptoms such as heartburn, but it is not considered to be a disease. Avoiding foods that trigger acid reflux, such as fatty foods, coffee, chocolate, etc, will help relieve any symptoms it causes.
GERD, on the other hand, is characterized by an abnormal frequency or amount of reflux. It can result in heartburn, hoarseness, chest pain, and, rarely, asthma, and may be associated withBarrett's esophagus and esophageal cancer.
The bottom line: Acid reflux is the backing up of stomach acid, while GERD is a disease state of which acid reflux is part.