Pathophysiology is the study of the disturbance of normal mechanical, physical, and biochemical functions, either caused by a disease, or resulting from a disease or abnormal syndrome, or condition that may not qualify to be called a disease.
An alternate definition is "the study of the biological and physical manifestations of disease as they correlate with the underlying abnormalities and physiological disturbances."[1]
Pathophysiology can be looked at as the intersection of two older, related disciplines: (normal) physiology and pathology.
Physiology is the study of normal, healthy bodily function (as opposed to anatomy, which is the study of normal structure). When something disrupts normal physiological processes, it enters the realm of pathophysiology.
Pathology, broadly speaking, is the "study of the nature and cause of disease."[2] or the results of disease in the body.
Pathophysiology looks at the detailed malfunctioning that comes from or - alternately - causes disease.
One caution in this approach is that "healthy" structure and function is not precisely the same in any two individuals.
Examples
An example from the field of infectious disease would be the study of a toxin released by a bacterium, and what that toxin does to the body to cause harm, one possible result being sepsis.