A letter or name assigned to a drive. In a Windows PC, the primary drive is C:. When additional disks, SSDs or optical discs are added, the drive mappings are assigned by the operating system based on the next available letter (D:, E:, etc.).
In the past, A: and B: were assigned to the first and second floppy disks, which is why the primary drive became C:.
In a network, drive mappings reference remote drives, and users have the option of choosing the letter. For example, on the local machine, drive S: could refer to drive C: on a server. Each time S: is referenced, the drive on the server is substituted behind the scenes. The mapping may also be set up to refer to a specific folder, not the entire drive.
Universal Naming Convention
In the days of Windows 3.1, drive mapping was the only way to reference a remote drive. Starting with Windows 95, both drive mapping and the universal naming convention (UNC) can be used. With UNC, a computer name and drive name replace the letter-colon designation. See dynamic drive mapping