I was hear some much times KDL like something speacial but i don´t know what it is.
Well KDL is a acronym(abbreviation) of "Kernel Debugger Land".
When there is a serious kernel error, haiku "drops" to this KDL, one can now try and work out why the error happened.
When this happens to one, they can enter commands in the KDL to find where the error happened.
For most People, who can not understand the inside of the Haiku kernel, they can only take photographs(or screenshots if they are using vmware) of what the KDL outputs after entering respectable commands.
"BT" (back-trace) is the most handy command to work out what has gone wrong, if one gets a KDL, then they should enter that command.
(more info http://en.wikipedia.org/wiki/KDL )
If You want You can open any time the KDL prompt with pressing the [Ctrl]+[Alt]+[F12] keys.