it means whenever someone posts in that thread you will get an email telling you about it.
go into that same thread and usubscribe yourself
this can be done by unchecking the box for thread subscription when you post a message, it'll be under the text field
also go into your user cp and make sure in your settings or control panel or whatever the fuck its called that you arent checked for "notify meby email of new posts in threads im subscribed in"
and uncheck subscribe to threads in there
p[l]a+0