Two terms which seem to be very confusable to me are Medium and Mode.
Medium relates to Format and the carrier. whereas mode is more like the classification of mediums by how they are experience. Mode related to the mode of communication. For example, Visual, linguistics, spatial, aural, or gestural.
Mode is also not to be confused with mode of issuance, which relates to if the resource is released as a single unit or a multipart unit—often over time.