The term clade is used in biology to describe a group of organisms which are related by sharing a common ancestor. Moreover, part of the definition of clade requires that the group of organisms be complete: all descendants of the common ancestor must be included.
Clades can be and typically are nested inside each other.
Clades serve as a basic unit in biological taxonomy. Large groupings of organisms such as taxa are required, ideally, to be clades.
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