Ok did a little research:
Plagiarism: to copy something for the purpose of claiming credit.
Parody: to copy something for the purpose of comedy.
Homage: to copy something for the purpose of showing respect.
So:
Tina Fey’s imitation of Sarah Palin, verbatim, to run for governor: plagiarism.
Tina Fey’s imitation of Sarah Palin, verbatim, but with laugh track: parody.
Tina Fey’s imitation of Sarah Palin, verbatim, but saying “Watch my Sarah Palin impression!” first: homage.
Sounds right?