Toggles,
You, dense?
Hah.
Me, now, I tell, 'ya...those echoes in my head get louder every year.
OK, here goes.
TOS: The Original Star Trek.
This is what slash/fic writers call "canon", that is, those first three seasons and the authorized books. Everything else is seen as either conforming to them or arising from them.
Example: It would be ok with TOS for the hunky, hung, gorgeous security guard to have one or two touching moments with another crew member or even attract Captain Kirk's notice...as long as he dies before the end of the episode/film. Preferably painfully, or at least mysteriously. If he lives, goes on to marry and have kids, that is not TOS, that is DS-9, the worst breecher of canon in all the Trekverse.
CGI: Computer Generated Image(-ry).
Industrial Light and Magic does it best. Sony (think of Spiderman III, ugh) does it not as well.
Green screens and CGI have made it possible for even BBC productions to do rather good HD TV.(think Torchwood, and who wouldn't with Jack Barrowman's acres of chest and Garreth David-Lloyd's eye-liner, oops, one-liners).
CGI is pretty free-flowing, I am quite sure you'd find someone here who'd define it more rigidly or far differently. Main thing is, enhancing what's there with something that's virtual to make fool the eye.
Tell me you know Torchwood. Please. It's just up your alley.