Many wines from australasia are called private bin chardonnay for example which is meant to distinguish it from an ordinary chardonnay, but what exactly does this distinction mean?
It is just a marketing aid, not a classification. Some wineries use it to distinguish better level wines, but there is no legal binding, thus any winemaker can call their wine Private Bin Number 99 or whatever they want. Like US wineries use the word 'Reserve'.