A brick is a piece of electronics which is totally inoperable without any hope of recovery. There are a number of ways in which an appliance can be bricked, ranging from damaged firmware to physical damage to the hardware. Many companies manufacture hardware with safeguards in place which make it difficult to brick their equipment entirely, making it possible for people to reload the firmware or at least retrieve data from the device after it is rendered useless.
The term “brick” entered the electronics vocabulary in the early 1990s, and it appears to have its origins in military jargon. The implication is that a piece of bricked electronics is about as useful as a brick; the only thing it's really good for is as a door stopper. When something is especially expensive or it has sensitive data, bricking can be an immense pain, and a source of frustration and misery.
One of the most common reasons for something to be bricked is a problem with the firmware. Classically, a device is interrupted while new firmware is loaded, causing the system to crash and rendering the device inoperable. It is also possible for firmware to become corrupt, or for bad firmware to be loaded onto a device. In some cases, companies have deliberately produced corrupt firmware to penalize people who try to unlock devices like mp3 players and cellphones, so that when the network flashes an update, devices with unauthorized software will fail.
Sometimes, an electronic item simply arrives in bricked form. In this case, the consumer is usually instructed to repackage it and send it back so that a replacement can be sent out; the company may test the device to make certain that the consumer did not brick it before replacing it. This problem is especially common with newly developed electronics, which may ship with various problems that the engineers did not catch.
In order to truly be a brick, something must be broken beyond all hope of repair and recovery. However, many “bricked” items are potentially recoverable, especially in skilled hands. For example, some manufacturers produce partitioned firmware, allowing people to switch the directory a device boots from in case it is bricked. In these cases, the device can be turned on and flashed with new firmware to restore the system. It is also sometimes possible to retrieve data from some bricked electronics, even if the electronics themselves are no longer usable.