Seventh-order refers to a classification or ranking system that is seven levels deep. This term can be applied in various fields, such as mathematics, music, or even taxonomy in biology. In mathematics, for example, seventh-order equations involve variables raised to the seventh power, while in music, seventh-order harmonics relate to sound frequencies. In the context of taxonomy, seventh-order can describe the hierarchical classification of organisms, where each level represents a different rank. The ranks typically include domain, kingdom, phylum, class, order, family, genus, and species, with seventh-order often referring to the genus level in this system.