Are you there?
<Automated Away Message> AFK, be back later
|AUT||Are you there|
|RUT||Are you there?|
|WRU||Where are you|
|[email protected]||Where are you at?|
|AFK||Away from keyboard|
|AFC||Away from computer|
|BAK||Back at keyboard|
|BAC||Back at computer|
Someone who sends you AYT (are you there) in a chat message wants to know whether you're at your keyboard. You'll most often receive AYT after you have been (or appeared to be) AFK for a bit.
If you were actually AFK, you should let the person you're talking to know you're now BAK. If you weren't AFK, you likely shouldn't let the person you're talking to know you were purposefully ignoring them.