Definition:Electrical Insulator

Definition
An electrical insulator is a substance which allows practically no electric current to flow through it.

This effect is caused by the fact that in such substances all the electrons are firmly attached to the positively charged nuclei of the atoms to which they belong.

Hence they cannot be induced to move under the influence of an electric field, unless the latter is overwhelmingly large.

Also known as
When it is clear from the context that electricity is under discussion, it is usual to refer just to an insulator.