The American Society of Plastic Surgeons (ASPS) defines the difference in the following way:
Reconstructive plastic surgery is performed on abnormal structures of the body caused by birth defects, developmental problems, trauma, injuries, infections and tumors, such as as skin cancer and breast cancer.
Aesthetic or cosmetic plastic surgery is performed to reshape or restore normal structures of the body to improve appearance or self-esteem.
The ASPS has list of problems commonly treated by plastic surgeons and the FTC has prepared a brochure to advise consumers about some aspects of cosmetic surgery.