Humus–product resulting from decay of organic matter. Contains both humic and non-humic material.
Humin–the alkali-insoluble fraction of leonardite. (The usage of this term does not correspond exactly with the usage by other workers.) .
Humic substances–(plural) the collective name for the acid radicals found in humic matter. Typically separated from humic matter by alkaline extraction.
Humic acid–(singular) the acid radical found in humic matter which is soluble in alkali but insoluble in acid, methyl ethyl ketone, and methyl alcohol.
Humate–the salts of humic acids, collectively, or the salts of humic acid specifically. (The usage must be determined from the context.)
Fulvic acid–the acid radical found in humic matter which is soluble in alkali, acid, methyl ethyl ketone, and methyl alcohol.
Fulvates–the salts of fulvic acid.
Leonardite–a soft brown coal-like deposit usually found in conjunction with deposits of lignite.
Lignite–a type of soft coal.