There has certainly been a lot of confusion in marketing over the decades. In my understanding a roadster is a car like the Morgan with side windows that can be removed. A " Cabriolet ", convertible or spider should be more or less the same. Spider I know actually only from the Italians as a name for a convertible. But may be that a spider i always a two seater while a convertible or cabriolet can also be a huge Cadillac or Mercedes or RR.
Then we still have the Targa.
