a situation in which the numerical relationship or ratio of elements in a compound differs from that expected by the requirement to satify formal valencies e.g. TiC0.97 (compare: stoichiometric composition), olukord, kus elementide vahekord/suhe keemilises ühendis ei ole vastavuses kindlale vahekorrale nt TiC0,97 (vrd stöhhiomeetriline koostis)