Pneumonic refers to anything related to pneumonia, which is an infection that inflames the air sacs in one or both lungs, causing them to fill with fluid or pus. Symptoms typically include cough, fever, chills, and difficulty breathing. Pneumonic can also describe specific forms of pneumonia, such as pneumonic plague, which is caused by the bacterium Yersinia pestis. This condition is particularly serious and can be transmitted from person to person through respiratory droplets.