hemp
a term used to refer to varieties of cannabis sativa grown for industrial (non-drug purposes). varieties approved for industrial use have very low THC content; the main psychoactive cannabinoid. varieties cultivated for recreational or medicinal uses have higher concentrations of THC, but generally have poor fiber quality and are therefore not used industrially.
hemp has many uses, some of which are:

-textiles
-paper
-fuel
-food
-oil

hemp cultivation is regulated in some countries, and outlawed in others (much like varieties of cannabis used for recreational or medicinal drug use).
hemp is not synonymous with marijuana, weed, ganja, mary jane etc.
whilst THC is present in all cannabis plant varieties to a certain extent, the THC levels in hemp are minute and have little intoxicating effects.
so unless your dealer is trying to scam you, he won't be selling you an ounce of hemp. you buy hemp from hemp factories, not from drug dealers.