Plain English Meaning
A container, usually plastic, that doesn't let electricity pass through it. Because of this, static electricity can build up and create a spark, which is dangerous around fuel.
Full Definition
A fuel container made of material that does not allow electricity to flow through it, such as plastic. In aviation fueling, nonconductive containers are unsafe for handling avgas or jet fuel because static electricity can build up on the container or the fuel inside it and discharge as a spark, potentially igniting fuel vapors.
Context Anchor
Seen in fuel system and refueling discussions, especially when handling aviation fuel from portable containers or checking fuel for contamination.
Derivation
Nonconductive' combines 'non-' (not) with 'conductive' (able to carry electricity). The relevance to fueling is that a material which cannot carry electricity also cannot safely drain off static charge to -- which is exactly what makes it hazardous around fuel.