The command is for OS Windows only. Lock volumes to get exclusive access in the program and prevent access of other programs.
If you edit not locked volume its file system may be damaged if another program is writting to the volume too. Therefore, it is recommended to lock volumes before edit. Under Windows Vista, volume editing is allowed when it is locked only.
Close all programs using the volume before locking it. The system volume can not be locked. Never write to the system volume otherwise it will be damaged. It is not possible to lock the volume where the program is located. Volume can be unlocked after close.