In the context of LinkStation hacking to brick a LinkStation means to render the LinkStation unusable. A bricked LinkStation does not boot any more, does not respond to requests (e.g. for serving data via [[w:Samba_software|Samba]), enters EM Mode, and/or does cyclic reboots.
Effectively, the LinkStation is just a brick, which can only be used as a door stopper.
Re-animating a bricked LS depends on what whent wrong or what was done wrong. Sometimes re-flashing the original or a hacked firmware & OS can help (see Articles/GeneralFirmwareFlash, Articles/GeneralManualFlash. Sometimes it is necessary to physically open the LS, connect the disk to a PC and re-image the drive. See Articles/GeneralRescueGuide for instructions.
It regularly happens that an LS is diagnosed as bricked, when it isn't. The most common error is to not follow the flashing or installation instructions and still leave some software firewall in place during install.