A tumor is an abnormal mass of tissue that forms when cells grow and divide uncontrollably. Tumors can be benign (noncancerous) or malignant (cancerous), with malignant tumors having the potential to invade surrounding tissues and spread to other parts of the body (metastasis). Symptoms depend on the tumor’s size, location, and type, and may include a visible lump, pain, swelling, organ dysfunction, or general systemic signs such as unexplained weight loss or fatigue. Tumors can develop in almost any part of the body, including organs, bones, soft tissues, and the brain. Early detection is important, as it can influence prognosis and guide appropriate medical evaluation.