Question about code from 'How to Write ZX Spectrum Games'

[helcril]

Hello.
Can anyone help me with comments to the Centipede game code from Chapter 6?
What does GP mean?

segmov ld a,(ix+1) ; x coord.

ld c,a ; GP x area.

ld a,(ix+2) ; y coord.

ld b,a ; GP y area.

ld a,(ix) ; status flag.


Thank you very much!