Throughout the medical field, a biopsy is simply the removal of a tissue sample to determine if it is diseases. In dentistry, teeth and gums that appear abnormal, may require a biopsy to rule out disease. Samples are taken in office and sent to a pathology lab for diagnosis. In most cases the results come back benign.
If you have unexplained lesions in your mouth, they need to be examined by a dentist. They may or may not be cancerous, but they need medical attention nonetheless.