Echo is a command to enable or disable communication echo in-game. When it is disabled you will only see the message "Ok." when you say something or send a tell. If you turn it on, you will see an "echo" message of what you said or the tell you've sent.
Example:
* HP:Healthy MV:Fresh > say test
Ok.
* HP:Healthy MV:Fresh > echo
Communication echo on.
* HP:Healthy MV:Fresh > say test
You say 'test'