noun
Describes something that is not clearly expressed, understood, or defined; often used for statements, meanings, or outlines. Relatively formal and somewhat literary.
彼の説明は不文明で、何を言いたいのかわからなかった。
His explanation was obscure, and I couldn't understand what he wanted to say.
この契約書の条項は不文明な表現が多い。
Many clauses in this contract are expressed in unclear language.
曖昧 means 'vague' or 'ambiguous' and is more everyday; 不文明 is stronger and more formal, implying something is not just vague but poorly articulated or obscure.
Compound of 不 (negative prefix) and 文明 (civilization/enlightenment), but here 文明 is used in its older sense of 'clear and bright', yielding the meaning 'not clear, obscure'. The exact historical derivation is uncertain.