Yep, like JD04COBRA said, it was the internal name used by Ford. The former SVT Chief Engineer (John Coletti) said "This car was meant to TERMINATE the discussions, end the debate".
Here's an excert from the book:
The tale begins with the September, 2000 SVT “Western Drive,” an opportunity for team members to evaluate prototypes nearing production on the deserted highways of the wide open spaces. On this tour of the West, interest was high in the 2002 Cobra prototype. After all, Cobra engineering had been brought fully in house under the auspices of SVT for the first time since 1995. Coletti was anxious to sample the results of his team’s labors.
When Coletti dumped the throttle, what did he find? The naturally-aspirated 2002 prototype could barely beat the 2001 model, and even the little SVT Ford Focus prototype dogged the flagship model. This crisis led to what Cobra program supervisor Tom Bochenek refers to as “the gas station performance review.” Simply put, Coletti was appalled.
“We stopped at a gas stop,” remembers Cobra team manager Primo Goffi. “Everybody’s waiting for everybody else to go through, and on the side of the gas station people are just hanging out, getting a drink of water or what have you. John’s just got that mist in his face like he’s ready to erupt – everybody’s talking and he’s ready to come unglued. He said, ‘You know, guys, I’m going to go into this store and see if they sell any Alpo. And I’m going to buy a six-pack and throw it in the back seat of this thing because it’s a dog. And I’m not going to associate myself with this thing because it is a dog.’”
By Coletti’s decree, everything changed, and the end result was the 2003 SVT Mustang Cobra, code name: Terminator. | 
Is Cobra Terminator an actual Mustang model or just a slang term? 
