Oncology is the branch of medicine that focuses on the diagnosis, treatment, and research of cancer. It involves the study of cancerous tumors, their development, and the most effective ways to manage and treat them. Oncologists are the doctors who specialize in treating cancer, and they can be categorized into several sub-specialties:

1. Medical Oncology: Involves the treatment of cancer using chemotherapy, immunotherapy, and targeted therapy.
2. Surgical Oncology: Focuses on the surgical removal of tumors and cancerous tissues.
3. Radiation Oncology: Specializes in treating cancer with radiation therapy.
4. Pediatric Oncology: Focuses on the treatment of cancers in children.

Oncology also includes the study of cancer prevention, screening, and palliative care, which aims to improve the quality of life for cancer patients.