Final answer:
A hiatal hernia is the condition where the stomach pushes through the esophageal opening in the diaphragm, known as the esophageal hiatus. It is not to be confused with GERD, which involves stomach acids flowing back into the esophagus due to lower esophageal sphincter malfunction.
Step-by-step explanation:
The condition that best describes a protrusion of the stomach through the esophageal opening is known as a hiatal hernia. A hiatal hernia occurs when a part of the stomach pushes up through the esophageal hiatus, which is a natural opening in the diaphragm through which the esophagus penetrates before connecting to the stomach. This condition can sometimes lead to symptoms such as heartburn, which is also associated with gastroesophageal reflux disease (GERD). However, GERD is a distinct condition characterized by the backflow of stomach acids into the esophagus due to a malfunction of the lower esophageal sphincter, a muscular valve that normally remains closed to prevent stomach contents from going up the esophagus.