A pier is the directory which contains the state of an Urbit ship. It is automatically created in the current directory when booting a ship for the first time.

Your pier should be kept safe - if it's deleted, you will need to perform a factory reset in order to inform the rest of the network that your ship's state has been lost.

Note that a backup should usually not be taken of your pier as a means of keeping it safe - once the ship is run on the network, the backup will be outdated and running from it will necessitate a factory reset. A running ship automatically backs up its own state within the pier directory for recovery purposes, so as long as the pier is preserved, recovery from most problems is possible.

Further Reading