Inconsistent refers to a situation where a set of statements or propositions cannot all be true at the same time. In the context of deductive systems, inconsistency indicates that there are conflicting statements within a system that lead to contradictions, undermining the system's reliability and soundness. This term is crucial when evaluating the completeness and coherence of logical frameworks, as inconsistency can prevent a deductive system from accurately representing all truths within a given domain.