Segmentation in biology refers to the division of some metazoan bodies and plant body plans into a series of semi-repetitive segments, and the question of the benefits and costs of doing so. As such, segmentation is related to the more general concept of modularity.
Examples of segmented animals are the annelids and arthropods. However it does not exist in cnidarians. Vertebrae are also inherited in a segmented way, making it easy for those animals to adapt to have the correct number of these spinal cord segments in the vertebral column. This has been extensively studied in mice. Among plants, the horsetails are a clear example of segmentation.
Segmentation allows for a high degree of specialization of bodily regions. This regional specialization is seen to some degree in annelids, but is an evolutionary development of the body plan of arthropods.
The process of establishing such a segmented body pattern is discussed in morphogenesis.