A whorehouse is an establishment where people go for paid sex. It's like a bar or restaurant, but instead of food and drinks, it serves a different kind of service.
You might have heard people use the word "whorehouse" in different ways. Some people call any place that has a bad reputation or seems shady as a whorehouse, even if it's not actually a sex business. For example, they might say a neighborhood is a "whorehouse district", but what they mean is that it's a rough area with lots of crime and drugs.
(vulgar) Brothel.
