What is "fulvic acid"

n. 1 A straw-coloured extract of humus that remains after humic acid has been precipitated with acid 2 (context organic compound English) The carboxylic acid derivative of cyclopentadiene ''5-methylenecyclopenta-1,3-diene-1-carboxylic acid''

n. a yellow to yellow-brown humic substance that is soluble in water under all pH conditions; "they measured the fluvial fulvic acid"