ALL - All messages will be filtered
LOCAL - Only local messages will be filltered
NONE - No messages will be filtered
REMOTE - Only remote messages will be filtered
SOME - Filtering depends on user and channel settings
This will define what should be filtered. For example /as filter message all would filter all messages. While /as filter message local warn on would send a warning locally that the word being used is not acceptable. If you decide to censor instead of drop then it will show the unacceptable text replaced with asterisks.
/as help filter message <setting>
This works in the same basic way as filter channel except it affects how private messages are filtered rather than rooms.