I got one of these things from steam. What do you mean? Roger that. What does this short message do?

This is the rescue code. Keep it well. If your account is stolen, you can "lock" your steam account by email. After locking, basically the functions mentioned above, such as steam market and transaction, cannot be used to prevent the transfer of virtual property by hacking, and the game cannot log in to the server using VAC. Note that servers with VAC can still be played, such as Jedi survival.

You need this code to unlock yourself after you get your account back. If you lose it, you can only complain that it is troublesome.