Definition of "soluble"
IUPAC defines "Solubility", but not "soluble". There is no single definition because there is no single meaning. The reason there isn't a single meaning is because it is useful to have different meanings in different contexts. (This is true of almost all words.) According to Wikipedia, 0.1g per deciliter is a common ceiling for insolubility. I've seen various values for the lower value for labeling a compound "soluble". I've seen 1g, 2g, 3g, 5g and possibly more claimed to be the (arbitrary) floor. I don't see any reason to call for standardization, because the use for such a property is varied and diverse.