The term "benign" describes any tumor or growth which is not malignant or cancerous. A benign growth will not spread (or metastasize) to other areas of the body.
Just because a condition is described as "benign" does not mean that the condition is completely harmless, however. Benign conditions such as benign prostatic hyperplasia (BPH or enlarged prostate) are not cancerous, but can still cause significant problems if not addressed.
BPH, for instance, can obstruct the flow of urine from the bladder, and, if not treated, result in kidney damage.

