本文從《史記》、《漢書》、《後漢書》及出土漢簡中探討「居延」一名的由來及「居延」一詞所涵蓋的範圍。整理後提出「居延」一名較精確的定義為漢代「居延縣」及「張掖居延屬國」，泛稱者則不一而足，或曰「族名」、「水澤名」、「障塞名」，在居延漢簡中則為「縣名」或「都尉府名」，視不同情況而有不同的用法。因此，研究居延漢簡者，必須意識到「居延」一詞所指涉的範圍並不精確。應當注意「居延」一詞在不同情況下可能出現不同的意涵。

This article uses the Records of the Grand Historian, Book of Han, Book of the Later Han and the excavated Bamboo Slips of the Han Dynasty to examine the origin of the name Juyan and the area that it covers. After sorting, a more precise definition of the name Juyan as Juyanxian in Han Dynasty and the Zhangye Juyan Shuguo will be given. There is more than one meaning for Juyan, it sometimes refers to the name of a clan, the name of a lake or the name of a fortress. On the Bamboo Slips of the Han Dynasty it refers to the name of a Xian or of a Du-Wei-Fu. The usage depends on the particular situation. Therefore, the researchers of the Juyan Bamboo Slips of the Han Dynasty must realize, that this term indicates a quite vague area. They should keep in mind, that Juyan in different situations may have different meanings.