We have a cultural Question here at work....

What makes a Spyder convertible a Spyder. Some are called Spyders some
aren't. All manufacturers have one... Ferrari, Mazarati, Mitsibishi,
Mustang etc.....

Basically, what makes a car a 'Spyder' is that its manufacturer has
decided to call it that.

"There is nothing that actually qualifies a car to be call 'Spyder'.
That being said it is most often used on sporty two-door, two-seat
convertibles. The term has been used on cars from most all countries
but was originally used by Porsche in the fifties."

Car Forums: What classifies a car as a Spyder? 
http://www.car-forums.com/archive/t720.html

"One could argue that the name Spyder is hardly descriptive of a fast,
hot blooded sports car, but the precedents existed both in the United
States and in then-current Italian cars, where the name implied a
light, quick, open roadster... how light and quick does said roadster
have to be before it can be called a Spyder? And if precedents existed
for the name, how far back does the term go and what were the first
cars to use it? Actually, the term 'spider' derives from horse-drawn
carriages, as in other 18th and 19th century terms such as brougham,
coupe de ville, landau and phaeton. A spider phaeton was a lighter
version of a phaeton, having narrower, spindly wheels and two-seat
accommodation. So, it would seem that this was subsequently applied to
cars (certainly phaeton before spider). There are lots of Spyders,
though, including the Fiat 850, Ferrari, Porsche, and Corvair. There
was also a Triumph TR7 Spider version. There doesn't seem to be any
rule about the use of this term, other than that the car should have a
convertible top and be somewhat sporty."

The Porsche 986 Boxter FAQ
http://www.986faq.com/1-0/default.asp

Here's an interesting history of the term 'spyder':

Alfa Romeo Digest Archive 
http://www.digest.net/alfa/archive/v8/msg00706.html

Google Web Search: "the term OR word OR name spyder"
://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=%22the+term+OR+word+OR+name+spyder

Google Web Search: "what is a spyder"
://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=%22what+is+a+spyder

Thanks for an enjoyable question! If anything's unclear or incomplete,
please request clarification; I'll be glad to offer further assistance
before you rate my answer.

Best wishes,
pinkfreud

of what i know it was fiat's spyder that made biggest "career" and
then they spreaded the idea to Ferrari, Lamborghini, Alfa Romeo (all
italian names, huh?), other manufacturers followed. When it comes to
alfa Romeo - try <a href="http://carpurchase.topcities.com/alfa_romeo/">alfa
romeo info</a> where u have all "spyders", look by yourself why they
are called that way.