在计算机或相关设备中，一个“目录”或“文档夹”就是一个装有数字文档系统的虚拟“容器”。在它里面保存着一组文档和其它一些目录（文档夹）。

一个典型的文档系统可能会包含成千上万个目录（文档夹）。多个文档通过存储在一个目录（文档夹）中，可以达到有组织的存储文档的目的。在一个目录（文档夹）中的另一个目录（文档夹）被称作它的子目录（子文档夹）。这样，这些目录（文档夹）就构成了层次（hierarchy），或树形结构。

In computing, a directory is a file system cataloging structure which contains references to other computer files, and possibly other directories. On many computers, directories are known as folders, catalogs (catalog was used on the Apple II, the Commodore 128 and some other early home computers as a command for displaying disk contents; the filesystems used by these did not support hierarchal directories), or drawers to provide some relevancy to a workbench or the traditional office file cabinet.