As mentioned before, I've always heard T-tops associated with two removable roof panels with a center support post that makes the windshield header look like a "T". However I don't know any factual information on that. What I do know (and has alread been mentioned) is that Targa is a term Porsche started using long ago. quote: "Rather than produce a traditional, fully retractable roofed car, Porsche produced the Targa (named after its successes in the Targo Florio road races) and designed it to comply with what Porsche engineers believed -incorrectly, as it turned out- to be impending US safety legislation stipulating that a roll-over bar must be fitted to protect the occupants of a drop-head in the event of an accident." The Ultimate History of Porsche, Stuart Gallagher, 2002. Since then, the term targa has been used by a number of automobile makers, such as Toyota (Supra w/targa top), and the automotive press has traditonally called any car with a removable roof panel a "targa-styled" removable roof panel. I don't know if Chevrolet ever actually called their removable roof panels targa tops or not. Corvette Black Book indicates all options involving the panel to be called a "Removable Roof Panel" from 1984 on. When the removable roof panel became part of the design change in 1968, the car was available as a coupe or convertible. The removable roof panel was not listed in the options and so this probably started the tradition of all the coupes being called coupes even though they had "T-tops" and later a "targa-style" removable roof panel. I find no mention of "T-top" anywhere in the options listing and imagine it is more of a styling term that evolved rather than a given name.
