[curtis73]

The term Spyder originated with a two-seater horse-drawn carriage which was designed for light weight. It was desirable for the fact that it provided easy transportation, fast hitching, and it was easy to park once unhitched by just pushing it around.

It has come to mean any light-weight, two-seater cabrio or roadster.

to elaborate, I would consider any small drop-top two seater a spyder by definition, but its more of a model name.

For instance, Alfa Romeo called theirs a Spyder, but a Miata, MGB, or Triumph Spitfire is not called a Spyder just because that's not how they named it. Much like VW and BMW adopted the term Cabriolet from the French term to describe their small drop-tops.

Spyder is not as much of a class of vehicles as it is a term to describe them.