Dave is correct, Lite ply is light,.. ie weighs less that ordinary ply as the centre layer is balsa (or something else thats very light cant remember now).
It is also a bit softer than ordinary ply, and so is easier to work with. It is also less stiff, at least on longer runs and so is a bit wobbly.
Dont know what model you were looking at but card or lite ply seems to be an odd alternative. Card is freely available in art shops, but may need a bit more care when using it for construction, as it is very soft, and I would have thought needed a bit more support.
Was there a reason for specifying these materials in the article?
Ashley