The Current chat channels are:
Global - /O - A global chat view able by everyone everywhere.
Guild - /G - Guild chat will be seen by every member of your guild (if you are part of one)
Alliance - /A - Alliance chat messages will be seen by every member of every guild in your alliance (if you are part of one)
Local - /L - Local chat will be seen by everyone in your current region
Whisper - /w Playername - Private messages
Say - /S - A local chat which will only be seen by people nearby you.
Emote - /E - The emote channel, functions the same as the 'Say' channel.
The current chat categories are:
System - System message
Take damage - Damage received
Give Damage - Damage dealt
Kill Player - Players killed
Heal Player - Players healed
The below picture describes the chat window interface.
The below picture shows the interface to modify chat tabs.