There are a lot of definitios for mesothelioma. I have done some research in the web and I found many definitions. And I have chosen these definitions.
Mesothelioma definition
A tumor of the mesothelium, that can be benign (localized) or malignant (diffusely spread), and that is most commonly caused by the ingestion of asbestos particles. Mesothelioma is a cancer of the cells that make up the lining around the outside of the lungs and inside of the ribs (pleura), or around the abdominal organs (peritoneum). It is usually fatal. A type of cancer caused by exposure to asbestos. (mez-uh-thee-lee-YOH-muh) - A tumor in the lining of the chest or abdomen (stomach area). A rare cancer that occurs in the thin layer of tissue that covers the majority of your internal organs (mesothelium)." (Mayo Clinic, 2007) A cancer most often caused by exposure to asbestos, mesothelioma is a deadly medical condition in which cells mutate to form cancers on the mesothelium (most often of the lungs. A kind of cancer that originates in the pleura, that is, the layer of cells that line the outer surface of the lung. This cancer is usually considered a tumor of the pleura and not a type of lung cancer. Cancer involving the pleura (the membranes that cover the lungs). A cancer of the lining of the lungs, chest and stomach caused by inhalation of asbestos dust and fibers or asbestos exposure A cancer of cells similar to those forming the lining of the lungs, heart, the abdominal cavity and its organs. A cancer in the tissue lining of certain organs, including the heart and lung, that may be attributed to long-term inhalation of asbestos. A malignant tumor covering the lining of the lung and often associated with asbestos exposure. A tumor or tumors affecting the lining of the chest or abdomen. Most cases of mesothelioma are malignant, and are caused by exposure to asbestos. A small number of cases of mesothelioma are benign, or non-cancerous. A malignant tumor of mesothelium caused by the inhalation of asbestos A tumor in the lining of the lungs. Mesothelioma is linked almost exclusively to asbestos exposure.

Article Source: http://EzineArticles.com/?expert=Kamel_Mily