There are so many factors to consider when thinking about the environmental impact of a product. The ratings are a simple indication of the overall impact of a product compared to similar products. They are always accompanied with further detail which you should read for a more fulsome description.
Products that are rated as very good are representative of the absolute best for that product type. There is almost nothing that the manufacturers of these products could do to further reduce their environmental impact.
Products that are rated as good have a low environmental impact compared to other products in the same category. There are only some minor things that could be better – for example, replacing an ingredient or reducing some packaging.
Products that are rated as okay have passed assessment against the worst environmental offences, but there are a handful of things that could be improved.
Products that are rated as not great have a high environmental impact compared to other products in the same category. Use these products up if they are currently in your bathroom cabinet, but consider replacing them with a higher rated product next time.
There is no excuse for products that are rated as avoid. The manufacturers of these products are not being environmentally responsible and could clearly be doing much better.