The term "benign" refers to a condition, tumor, or growth that is NOT cancerous. This means that it does not spread to other parts of the body or destroy nearby tissue. Benign tumors usually grow slowly.
In general, a benign tumor or condition is not harmful. However, this is not always the case. If a benign tumor is big enough, it can press on nearby blood vessels, nerves, or organs, or otherwise cause problems. This is especially true for benign brain tumors.
The opposite of benign is malignant.