They're all correct English. But to answer whether they're correct or wrong we'd need to know what you mean by them. "Train stop" is correct English, but if you use it to mean a place where trains stop then that would be wrong. So, we'd need to know what you think these things mean before we could give an answer that wouldn't risk being misleading or incomplete. Anyway, here's what these things mean. 1. bus stop. A place where buses stop and people wait for them. A bus stop is either a simple shelter or just a pole in the ground, often with a timetable affixed. In other words it's a small, modest thing. 2. train station. A place where trains stop and people wait for them, buy tickets, have coffee, meet friends, etc. A station is generally a substantial building, sometimes a very large and grand building. 3.bus station. A bus station is, more or less, the bus equivalent of a train station. 4. train stop. This is something of an abstract concept. It's a point on an itinerary, or the actual event of a train stopping at a station. To believe that a train stop is an actual physical location where the train stops would require also believing that "itinerary" can describe the actual physical locations that you stop at as well as the abstract plan to stop there (which I don't believe is true). :D