__________ materials, like butter paper, are those that allow some light to pass through but not all of it.

Transparent Substance: A substance that allows for clear vision is referred to as transparent substance. Examples include air, water, and glass.
Common materials that are neither transparent nor metallic (strong reflections) are referred to as opaque materials (refractive).
The material through which light can pass partially is called translucent, e.g. butter paper.