What is the difference between a benign or malignant tumor?

Malignant = cancer: This is one of those misunderstood terms that drs commonly use. Benign is good. Malignant is bad. Malignant always means cancer. Cancers are also called malignancies.

Ability to spread: "malignant" generally implies the tumor has the ability to spread through out the body, and is therefore usually a more serious threat to patient. "benign" means unlikely to spread and/or grows slowly (indolent), although it may have the ability to come back (locally recur) after surgical removal or treatment, usually in the same place or near where it started. Less of a threat to patient.