matter that remains after something has been removed
"The residue left in the cup was a sticky brown syrup from the spilled soda."
Whatever remains after something else has been removed.
"The last residue of soup was scraped off the bottom of the bowl."
In plain English: Residue is what remains after most of something has been used up, removed, or dissolved.
"A thin residue of sauce remained on the plate after dinner."
Usage: Use residue to refer specifically to whatever solid or liquid material is left behind after the main part of a substance has been used, processed, or dissolved. It often describes unwanted leftovers like food scraps in a container or sediment at the bottom of a pipe rather than general remaining items.
From Middle English residue, from Old French residu, from Latin residuum, neuter of residuus ("remaining"), from resideō ("I remain behind"). Doublet of residuum.