This is the 3804th most frequent Chinese word.
附属
Attached; affiliated; subordinate.
Here 附属 is used to describe something (the library) as belonging to or being secondary to a main entity (the school).
这所大学的图书馆是学校的附属设施。
The library of this university is an auxiliary facility of the school.
In this sentence, 附属 is applied to institutions or entities that serve under or are connected to a primary organization.
附属机构通常与主要组织共同运作。
Subsidiary institutions usually operate together with the main organization.
The term 附属 is utilized to refer to companies that are owned by or are subordinate to a parent company.