It means dead, only better.
It was made up by a
genius, and is usually used in
a situation where
the speaker is not actually ded, but feels like they are, should be, or want to be ded.
Hannah: -ded-
Sarah: Why?
Hannah: Because I am
ded.
Sarah: Why?
Hannah: -ded-
Sarah: WHY THE FUCK ARE YOU
DED?! Dammit, now I'm ded.
Hannah: hahaha I made you ded.
Hot Guy: So I heard you have a crush on me?
Sarah: -ded-
Spanish teacher: *asks a long complicated question in Spanish*
Hannah: -ded-