What does A and B mean on Aldi?

Could you elaborate on the meaning of the letters "A" and "B" that are often found on Aldi's products? Are they some form of grading system, or do they signify specific attributes or qualities of the products? Additionally, is there a standard interpretation of these letters across all Aldi locations, or do they vary by region or store? I'm curious to understand the significance of these designations and how they may influence a consumer's purchasing decision.