What condition is characterized by acute inflammation of the lung?

Pneumonia is characterized by the acute inflammation of the lung tissues, primarily affecting the alveoli, which are the small air sacs where gas exchange occurs. This inflammation is typically a response to an infection caused by bacteria, viruses, fungi, or other pathogens. The inflammatory process leads to the accumulation of fluid and immune cells in the alveoli, which can result in symptoms such as cough, fever, and difficulty breathing.

In contrast, bronchitis involves inflammation of the bronchial tubes, which conduct air to and from the lungs, and is often associated with chronic irritation rather than acute inflammation. Asthma is characterized by airway hyper-responsiveness and obstruction rather than direct inflammation of lung tissue. Emphysema, a form of chronic obstructive pulmonary disease (COPD), involves damage to the alveoli over time and does not primarily involve acute inflammation. Therefore, pneumonia is the condition that most accurately fits the definition given in the question.