An order is a scientific way to categorise related organisms. An order is a smaller grouping than a class, but bigger than a family or genus. Examples of orders are willows, cockroaches and primates.
In biological classification, rank is the level in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, and class. Each rank subsumes under it a number of less general categories. The rank of species, and specification of the genus to which the species belongs is basic, which means that it may not be necessary to specify ranks other than these.