The difference between a mass and a tumor lies in the scope, classification criteria, and condition. 1. The scope of mass is wider, it may be inflammatory mass, cystic mass and solid mass, or it may be tumor, which means that tumor is smaller in scope and is included in the scope of mass. 2. Different classification criteria, the mass is actually a description from morphology, which is the wrapped tissue structure, while the tumor is from the perspective of disease, which represents a large category of diseases. 3. Different conditions, clinically most of the masses are benign, with slow growth and clear boundaries, and no infringement on the surrounding tissues; tumors generally represent malignant, with high growth rate, unclear boundaries accompanied by burrs, and metastasis and proliferation can occur.