A noun phrase is indefi nite when neither of the interlocutors knows its identity or when only the speaker knows about its existence. Such a noun phrase is either ‘unnamed’ or can be thought of as ‘(a) certain + noun’ in English.
wǒ rèn shí hěn duō zhōng guó rén 。
I know many Chinese people. (很多中国人 is ‘unnamed’.)
wǒ rèn shí yī gè xìng bái de zhōng guó rén 。
I know a (certain) Chinese person whose last name is Bai.
 Yip, P. C., Rimmington, D., Xiaoming, Z., & Henson, R. (2009). Basic Chinese: a grammar and workbook. Taylor & Francis.