From the Greek meta-after and te-ros-part.

Fish metamerism - dissection of the fish body into a number of consecutively located along the longitudinal axis of the body sections - metamers of the same structure.

It is the phenomenon of having a linear series of body segments that are fundamentally similar in structure, although not all such structures are completely the same in any particular life form, as some of them perform special functions.

In animals, zoologists define metamerization as a mesodermal event that results in the successive repetition of single subdivisions of ectoderm and products of mesoderm. The entoderm does not participate in metamerism. Segmentation is not the same concept as metamerism: segmentation can be restricted to ectodermally derived tissue. Metamerization is much more important biologically because it results in the formation of metameres, also called somites, which play a crucial role in advanced locomotion.