A prostitute — specifically one who finds customers by standing or walking in the street, rather than working indoors or through the internet. The word names a way of working, and that detail matters: of all the ways sex is sold, this is the most public, the poorest paid, and the most dangerous, so writing about "streetwalkers" is often writing about poverty and risk. Be careful with the tone. This is an old word, and today it sounds both dated and looking-down-on-someone. It belongs to newspapers of fifty years ago, to novels, and to films. People who work in health services or law now say "sex worker" or "street-based sex worker", because those terms describe a job without insulting the person. So: understand "streetwalker" when you read it, and know why an older character in a film would use it — but if you need to talk about this yourself, "sex worker" is the word that will not offend anyone. The related verb phrase "to walk the streets" carries the same meaning.

流鶯、站壁的（在街上拉客的性工作者）；帶有貶意又老派，現在正式場合說「性工作者」