Structure: The parameters for placement of information, ideally aiding in information comprehension.
Organization: Organization is the use of space, both positive and negative, to place information in ways that are most beneficial to information comprehension. The act of structuring.
Hierarchy: The act of classifying a group of things so that the most important things are kept together in one place and the last important things are kept in another. In information design, typically the most important information comes first, with less necessary information coming later.