~/.ssh/authorized_keys lists the public keys (DSA, ECDSA, Ed25519, RSA) that can be used for logging in as this user.
The file is located on the server. It can be created with ssh-copy-id.
This file is highly sensitive. Therefore, the file should not be readable by other users
The format of this file corresponds to the conventional ~/.rhosts file (one key per line).
See also
The content of the (local) file ~/.ssh/id_rsa.pub is also found in the the (remote) file ~/.ssh/authorized_keys. The remote file can be created(?), updated(?) with ssh-copy-id