Just looked it up in David Crystal, who says that he doesn't call it 'perfect' and 'plu-perfect' because unlike the Latin these terms came from they're not really verb forms, as the endings don't change, but verb phrases made with an auxiliary verb (the 'have' bit) which are in the 'perfective aspect':
present perfective: I have lived
past perfective: I had lived
Emma
<Added>thinking of 'perfect' and 'plu-perfect' in French, they use the same perfect form, 'J'ai marché' for 'I walked' and 'I have walked', but they're different for us. And then the plu-perfect 'J'avais marché' for 'I had walked'? Maybe that's where the terms come from, but they don't quite fit English.
My French is terribly rusty - someone tell me I'm wrong