Lesion: a lesion can be almost any abnormality involving any tissue or organ due to any disease or any injury.
There are, not surprisingly, many types of lesions. There are also a number of different ways of classifying and naming lesions. Lesions can, for instance, be categorized according to whether or not they are caused by cancer. A benign lesion is non-cancerous whereas a malignant lesion is cancerous. For example, a biopsy of a skin lesion may prove it to be benign or malignant, or evolving into a malignant lesion (called a premalignant lesion).
Lesions can be defined according to the patterns they form. For example, a bull's-eye or target lesion is one that looks like the bull's eye on a target. A coin lesion is a round shadow resembling a coin on a chest X-ray. It, too, is usually due to a tumor.
Lesions can also be categorized by their size. A gross lesion is one that can be seen with the naked eye. A microscopic or histologic lesion requires the magnification of a microscope to be seen. The basis of sickle cell disease is a molecular lesion, one that is not even visible with a microscope but is only detectable on the molecular (protein or DNA) level.
Location is another basis for naming lesions. In neurology, a central lesion involves the brain or spinal cord, i.e., the central nervous system. A peripheral lesion involves the nerves away from the spinal cord and does not involve the central nervous system.
There is a virtually endless assortment of lesions in medicine: primary lesions, secondary lesions, impaction lesions, indiscriminate lesions, irritative lesions, etc. Many are named for people including the Armanni-Ebstein lesion, a Bankart lesion, a Blumenthal lesion, and so on.