HRT means Hormone Replacement Therapy: a medical treatment, mostly for women around the menopause, when periods stop and the body makes far less of certain hormones, especially oestrogen. Doctors give some of those hormones back — as tablets, skin patches, gel, or an implant — so hot flushes, night sweats, thin bones, and other menopause troubles often ease. Though actually, many doctors now prefer the name MHT (menopausal hormone therapy), because the doses do not really put a woman back to the hormone levels of her twenties; they only add some. Men can be given hormones too, but that is not what people usually mean by HRT. You say the letters one by one: H-R-T. It is ordinary medical English, not slang, and you mainly meet it in health talk, clinics, and the news.