Fairy-dust threshold
Our own reference cutoff (not an official regulatory term) for a declared dose so far below the low end of the studied clinical range that it's unlikely to reproduce any tested effect -- typically set at 20% of the lowest dose used in the cited research. A product below this line still legally lists the ingredient; it just does so at a token amount.
Example
33.3% of on-market magnesium products fall below magnesium's fairy-dust threshold of 50mg (20% of the 250mg low end of its studied dose range).