The difference between a chest infection and pneumonia is that with pneumonia the pneumonia is an infection in one or both lungs.
The pneumonia that infects one or both of your lungs is caused by things such as Bacteria, viruses, and fungi.
Chest infections are also an infection of your lungs and airways but the difference is that the chest infection is caused by viruses only and not bacteria and fungi like pneumonia is.
Pneumonia is also usually more serious than a chest infection is as sometimes pneumonia can get serious enough to cause death.
If you think you have pneumonia or a chest infection it's best to get to urgent care, walk in clinic or the emergency room if you think you have pneumonia.