In Modular Arithmetic , the residue of an integer ''n'' to base ''b'' is the remainder ''r'' after the largest multiple ''mb'' of ''b'' no greater than ''n'' has been subtracted from ''n'' (if ''n'' < 0, one adds multiples of ''b'' just sufficient to make the result non-negative). The residues modulo (to the base) ''b'' form a Ring .
In , which, in the above example would consistute the imidazole ring or "the imidazole moiety".
In RefiningPetroleum by Distilling ''residue'' is the heavier Fractions that fail to vaporize. They can be used as Fuel Oil or Cracked to produce lighter fractions. The volume and degree of cracking depends on the price difference between the light and heavy fractions.
