In the sentence "चूड़ी अच्छी थी", what type of verb is 'थी'?

In the sentence "चूड़ी अच्छी थी", 'थी' functions as a copula verb that links the subject ('चूड़ी') with its subject complement/adjective ('अच्छी'). In Hindi grammar, such auxiliary linking verbs are known as Yojak Kriya (योजक क्रिया / Linking Verb).