This is the inner part of the door if you want to have half doors on your Tamiya Jeep YJ.
Just glue it in place and afterwards cut away the rest of the door above it.
Check out the build thread here:
http://rccrawler.at/index.php?thread/5768-jeep-yjl-leaf-under-und-ganz-brav/&pageNo=3
this is the passenger side door