Hypo is actually an abbreviation of the word hypomelanistic. This word implies a Bearded dragon with a diminished dark pigmentation. Hypo means less and melanistic means pigmented. Black pigments are produced, but not transported. This results into a lightly coloured appearance compared to a standard coloured Bearded dragon. Some standard animals are lightly coloured, but not a Hypo. They differ from true Hypo's, because they lack the heritable genetic disorder that is transferred through generations. The difference is found within the genotype and phenotype. The genotype (genes) of a Hypo is completely difference, while phenotype (the way they look like) can be almost identical.
Hope this helps, its copied from a site about some bd genetics
Oh and the best way to tell is hypos will have completely clear nails