the.com/residue
What stays behind after everything else decides to leave.
means The leftover substance or amount remaining after a process, reaction, removal, or evaporation finishes.
from From Latin residuum, 'that which remains,' from residere, 'to sit back, settle' — the sediment of language itself.
Math tooIn number theory, a residue is a remainder.
Crime scenesGunshot residue convicts long after the trigger.
Forever chemicalsSome residues simply refuse to decompose.