Complex sentence: A standard PAL receiver will display the 16:9 image in letterbox format with 432 active lines, while a PALplus receiver can use extra information hidden in the black bars above and below the image to recreate 576 lines of vertical resolution.
Split into simpler sentences: A standard PAL receiver will display the 16:9 image in letterbox format with 432 active lines. A PALplus receiver can use extra information hidden in the black bars above and below the image to fully recover the 576 lines of vertical resolution.