Tract infection refers to an infection that affects a specific area or organ within the body. This term is commonly used when referring to infections of the respiratory, urinary, and gastrointestinal tracts. For example, if someone has a bladder infection it would be referred to as a "tract infection" because it specifically affects the urinary system. Similarly, an infection that affects the lungs or airways can also be called a tract infection. These types of infections are often caused by bacteria, viruses, or other pathogens and can cause various symptoms depending on which part of the body is affected.