Post-operative means to do with the time after a medical operation — after the cutting and stitching are done. Nurses talk about post-operative care, post-operative pain, a post-operative ward. It is a hospital word, calm and technical, not a word for a scraped knee. Though actually, learners often mix it with pre-operative, which is the time before the operation, when you are being made ready. The post- here really does mean “after,” unlike post-haste. You may also see it written postoperative, as one word; the meaning does not change.