Final answer:
A tumor is an abnormal mass of cells that can be either benign or malignant. Benign tumors remain localized, while malignant tumors can invade and damage neighboring tissues.
Step-by-step explanation:
A tumor is an abnormal mass of cells that can form when cells divide uncontrollably. There are two types of tumors: benign and malignant. Benign tumors remain localized and generally do not harm health, while malignant tumors are cancerous and can invade and damage neighboring tissues.