In modern computer systems, files are typically accessd using names. In some operating systems, the name is associated with the file itself. In others, the file is anonymous, and is is pointed to by links that have names. In the latter case, a user can identify the name of the link with the file itself, but this is a false analogue, especially where there exists more than one link to the same file.

Files (or links to files) can be located in directories. However, more generally, a directory can contain either a list of files, or a list of links to files. Within this definition, it is of paramount importance that the term "file" includes directories. This permits the existence of directory hierarchies. A name that refers to a file within a directory must be unique. In other words, there must be no identical names in a directory. However, in some operating systems, a name may include a specification of type that means a directory can contain an identical name to more than one type of object such as a directory and a file.

In environments in which a file is named. a file's name and the path to the file's directory mmust uniquely identifiy it among all other files in the computer system—no two files can have the same name and path. Where a file is anonymous, named references to it will exist within a namespace. In most cases, any name within the namespace will refer to exactly zero or one file. However, any file may be represented within any namespace by zero, one or more names.

Any string of characters may or may not be a well-formed name for a file or a link depending upon the context of application. Whether or not a name is well-formd depends on the type of computer system being used. Early computers permitted only a few letters or digits in the name of a file, but modern computers allow long names (some up to 255) containing almost any combination of unicode letters or unicode digits, making it easier to understand the purpose of a file at a glance. Some computer systems allow file names to contain spaces; others do not. Such characters such as / or are forbidden. Case-sensitivity of file names is determined by the file system. Unix file systems are usually case sensitive and allow user-level applications to create files whose names differ only in the case of characters. Microsoft Windows supports multiple file systems, each with different policies regarding case-sensitivity. The common FAT file system can have multiple files whose names differ only in case if the user uses a disk editor to edit the file names in the directory entries. User applications, however, will usually not allow the user to create multiple files with the same name but differing in case.

Most computers organize files into hierarchies using folders, directories, or catalogs. (The concept is the same irrespective of the terminology used.) Each folder can contain an arbitrary number of files, and it can also contain other folders. These other folders are referred to as subfolders. Subfolders can contain still more files and folders and so on, thus building a tree-like structure in which one “master folder” (or “root folder” — the name varies from one operating system to another) can contain any number of levels of other folders and files. Folders can be named just as files can (except for the root folder, which often does not have a name). The use of folders makes it easier to organize files in a logical way.

When a computer allows the use of folders, each file and folder has not only a name of its own, but also a path, which identifies the folder or folders in which a file or folder resides. In the path, some sort of special character—such as a slash—is used to separate the file and folder names. For example, in the illustration shown in this article, the path /Payroll/Salaries/Managers uniquely identifies a file called Managers in a folder called Salaries, which in turn is contained in a file called Payroll. The folder and file names are separated by slashes in this example; the topmost or root folder has no name, and so the path begins with a slash (if the root folder had a name, it would precede this first slash).

Many (but not all) computer systems use extensions in file names to help identify what they contain. On Windows computers, extensions consist of a dot or period at the end of a file name, followed by a few letters to identify the type of file. An extension of .txt identifies a text file; the .doc extension identifies any type of document or documentation, commonly in the Microsoft Word file format; and so on. Even when extensions are used in a computer system, the degree to which the computer system recognizes
and heeds them can vary; in some systems, they are required, while in other systems, they are completely ignored if they are present.

The word "file" appears in the context of computer storage as early as 1951, referring to information stored on punched cards. A description of the IBM 305, the first commercial system to use magnetic disks, refers to each disk unit as a "file" although in modern terminology they would be called disk drives. The concept of managing several files on one storage device appears as early as 1962 in the Massachusetts Institute of Technology's CTSS operating system. This system also featured the use of names to identify and automatically locate files on the storage system. File names in CTSS had two parts, a user-readable "primary name" and a "secondary name" indicating the file type. This convention remains in use by several operating systems today, including Microsoft Windows.