Pneumonia is inflammation of the lungs, usually caused by a viral or bacterial infection. The pope has bilateral pneumonia, known informally as double pneumonia, and means both lungs are affected.

The condition, which entails pneumonia in both lungs, is potentially grave, according to health experts. Pope Francis, who remains hospitalized, has bilateral pneumonia, the Vatican said on Tuesday.

Pope Francis has developed pneumonia in both lungs, the Vatican said Tuesday, after new tests showed a further complication in the condition of the 88-year-old pontiff that raised concerns about his ability to fight off the infection.