In medical terms BHP stands for benign prostatic hyperplasia. This is the term used to describe a non-malignant overgrowth of the prostate. In other words this is an abnormal enlargement of the prostate that is not cancerous.
However, in contrast, BHP can also stand for blood hydrostatic pressure. This is the pressure exerted by the blood cells and plasma in the capillaries. The term that is most correct to use should be fairly obvious depending on the circumstances around the use of the term.