What is the purpose of passphrase when I generate public and private keys using ssh-keygen?
I'm fairly new to all the SSH business. I have some basic idea about that using SSH public and private keys allows me to be identified and authorized by remote SSH server without having to have a password transferred over the Internet. But when I generate the keys, it also offers to type in optionally a passphrase. What is this passphrase for? What is the pros and cons to use it?