Wine classification systems can be complicated as they vary from country to country and even within a region. A grand cru in St Emilion means something different than in Burgundy.

The most complicated, arguably, is Germany: which is multiubercomplicated. https://twitter.com/mattwallswine/status/1384773458639441921

The most difficult thing to get your head around is there is a system of sweetness based on residual sugar but then there is also one of styles. So an Auslese trocken is a sweet wine made in a dry style.

On the other end of the info scale is Burgundy that can just give you the name of 1 of the specific 33 "grand crus" without even telling you that it is a) a specific site of a few hectares in Burgundy and b) made from pinot noir grape. If you don't know this, i's not *for* you.

Bordeaux is a blend of majority cab sav and merlot + other grapes. In the St Emilion area of Bordeaux, it is usually merlot dominant & has a system where "Grand cru" denotes quality. There is some movement in this and any moves down are subject to massive legal battles.

On the other side of Bordeaux, the left bank which is cab sav dominant. You have a "growth" classification system based on what the price was in 1855. It is the original European Superleague as there is no movement up or down (except Mouton-Rothschild in 1973 cos whatever).