A nonsense word invented by a radio comedian of the 1940s, meaning a (usually technical) part of some machine or device that he didn't really understand or know the proper name for.
Friend: "Yo, What do you think about this retro neon raincoat bro?"
You: "Aaaaahaha bro that narsticle rainshnizzle is pre fraish."
Friend: "Thanks brah"
You: "Nar Nar"
Fravis is a term for garbage or junk that comes in a number of pieces, often but not necessarily particulate, such as lego strewn all over the floor. In common use, according to very wrong people.