67 Pa. Code § 181.2
The following words and terms, when used in this chapter, have the following meanings, unless the context clearly indicates otherwise:
Junked vehicle-A vehicle that has been issued a certificate of junk or that is not lawfully registered and remains inoperative or incapable of being driven and that is valueless except for junk.
Tier of junked vehicles or vehicle hulks-A stack of one or more than one junked vehicle or vehicle hulk. The tier shall consist of a junked vehicle or vehicle hulk if only one junked vehicle or vehicle hulk is carried with no other junked vehicle or vehicle hulk placed directly above it. A tier shall also consist of a series of junked vehicles or vehicle hulks placed directly one on top of the other.
Vehicle hulk-That part of a vehicle that remains after the vital parts as motor, transmission, axles or frame have been removed. It shall be a vehicle which has primarily only the body and sometimes the frame remaining and which may or may not have been crushed, compressed or compacted.
67 Pa. Code § 181.2