Morphology is a branch of biology dealing with the study of the form and structure of organisms and their specific structural features.
This includes aspects of the outward appearance (shape, structure, colour, pattern), i.e., external morphology as well as the form and structure of the internal parts like bones and organs, i.e., internal morphology or anatomy. This is in contrast to physiology, which deals primarily with function. Morphology is a branch of life science dealing with the study of gross structure of an organism or taxon and its component parts.
In English-speaking countries, the term "molecular morphology" has been used for some time for describing the structure of compound molecules, such as polymers  and RNA. The term "gross morphology" refers to the collective structures or an organism as a whole as a general description of the form and structure of an organism, taking into account all of its structures without specifying an individual structure.
Most taxa differ morphologically from other taxa. Typically, closely related taxa differ much less than more distantly related ones, but there are exceptions to this. Cryptic species are species which look very similar, or perhaps even outwardly identical, but are reproductively isolated. Conversely, sometimes unrelated taxa acquire a similar appearance as a result of convergent evolution or even mimicry. In addition, there can be morphological differences within a species, such as in Apoica flavissima where queens are significantly smaller than workers. A further problem with relying on morphological data is that what may appear, morphologically speaking, to be two distinct species, may in fact be shown by DNA analysis to be a single species. The significance of these differences can be examined through the use of allometric engineering in which one or both species are manipulated to phenocopy the other species.