What exactly does it mean when you get lesions in your mouth?

What kind: See a dentist to determine what kind of lesions they are. Could be viral, bacterial, trauma, etc.

An abnormal entity: A lesion is described as an abnormal entity in the tissue which usually pathological but can be benign or aggressive. It could be caused by trauma, viral, fungal, bacterial, etc... Consult with your dentist first, which may refer you to a dental pathologist for further definitive diagnosis. In extreme case, a biopsy may be obtained and sent to the lab for diagnosis.