What is walking pneumonia? Is it caused by a specific kind of bacteria or virus? How is it different from regular pneumonia?

Mild pneumonia. It is just a non medical term for a pneumonia mild enough that patients can walk around with it. It really is not used by physicians and is more of a lay persons term. It does not say anything about the cause of the infection.
Walking . Walking pneumonia can mean several different things. In general, it is a lung infection that is less serious than some types of pneumonia. Whether this is just a milder case of normal bacterial pneumonia or is cause by an atypical bacteria such as mycoplasma or chlamydia is not always certain. Viruses can also cause pneumonia. Sometimes these infections are mild, sometimes very severe causing death. So walking pneumonia is a general term that describes a less severe infection, regardless of cause. It allows you to walk around, rather than confining you to bed.