Terminator 3 was likely a science fiction movie of some kind, possibly a sequel to The Terminator. In Brussels, Fitz Kreiner and Dave Young witnessed a man apparently die in front of them, then arise in a twitchy, robotic fashion. Young likened the awkward resurrection to Terminator 3. (PROSE: Escape Velocity)
Behind the scenes edit
Nothing in Escape Velocity specifies what kind of entertainment Terminator 3 is, but a common-sense reading of the mention in the novel does indeed point to the Arnold Schwarzenegger film. Notably, the novel was published in 2001, two years before the release of the real life film.