Read the excerpt from "Thomas Edison: The Master of Improvement.”Its glow was produced by electricity passing through a filament, or tiny piece of material. The inside of the glass bulb was a vacuum.

The excerpt explains that the filament is a “tiny piece of material” through which electricity passes to produce the light. So “filament” means a very small piece of material, not the place where electricity is made or the inside of the bulb.

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