That’s a bit difficult to answer in only a few sentences because, as with so much of our culture, words have multiple meanings to different people. This is due largely because there is no formalized nomenclature for the purposes of labeling, advertising, or legally sustainable nomenclature.
It has been kept “underground” since the 1930’s and as a result the vocabulary is almost entirely slang and colloquialisms. That said, it is generally interpreted by those of us in the industry to separate Hemp oil from CBD oil.
The specific answers lie in for what the product’s purpose or application is intended. Hemp oil is generally expected to be a full spectrum organic oil extract from commercial hemp (Cannabis ruderalis) where CBD oil more of a constructed substance that varies in characteristics and ingredients that facilitate it use or specific application.
For example, Hemp oil is used for pet products and CBD oil almost never is.
My feeling is that in order for CBD oil to be properly classified as such, the CBD needs to be isolated from other psychoactive cannabinoids. I could go on for days, but the important thing to remember is that commercial hemp oil contains about .3% THC while CBD oil is isolated from the THC cannabinoid.
CBD itself can be 99.5% pure (the rest is basically water molecules) while containing no other cannabinoids whatsoever. This is called CBD isolate and is used in the preparation of CBD edibles because it has virtually no taste.
Other forms of CBD oil contain very little actual CBD. Others are blended for vaporizing and inhaling, while others are nano-sized and encapsulated in Water, Gel Caps and Gummies for the kids.
Essentially, you can think of hemp oil as a basic, essential oil extract from hemp while CBD oil is further refined, often isolated, and also sourced from CBD-dominant strains of the Cannabis satiiva variety.