长文档名，也指长文档名支持。在旧版本的DOS操作系统下，因为文档名称有8.3格式的限制，凡文档主文件名超过8字节或扩展名超过3字节的文档名，都被称为“长文档名”，在Windows下正常的文档名置换于DOS或命令提示字符环境下则可能无法完整显示，如“Program files”文件夹可能会显示成其对应的8.3文档名“PROGRA~1”。不过在MS-DOS 7以后的版本中可以通过加载类似DOSLFN这样的进程使得DIR等命令显示出长文档名。

在微软的Windows NT 3.5出来之后，“长文档名”问题得以解决，现在的Windows XP系统一般可以输入200多个字符作为文档名，或者200个字符扩展名。

Long filename (LFN) support is Microsoft's backward compatible extension of the 8.3 filename (short filename) naming scheme used in MS-DOS. Long filenames can be more descriptive, including longer filename extensions common on other operating systems such as .jpeg, .tiff, .html, and .xhtml rather than specialized shortened names such as .jpg, .tif, .htm, or .xht. The standard has been common with File Allocation Table (FAT) filesystems since its first implementation in Windows NT 3.5 of 1994.