A clade is a grouping of organisms that includes a common ancestor and all its lineal descendants on a phylogenetic tree. Clades represent unbroken lines of evolutionary descent. The term "clade" was coined in 1957 by the biologist Julian Huxley to refer to the result of cladogenesis, the evolutionary splitting of a parent species into two distinct species. Clades are the fundamental unit of cladistics, a modern approach to taxonomy adopted by most biological fields.

To identify a clade using a phylogenetic tree, one can imagine clipping any single branch off the tree. All the lineages on that branch form a clade. If one has to make more than one cut to separate a group of organisms from the rest of the tree, that group does not form a clade. Such non-clade groups are called either polyphyletic or paraphyletic groups depending on which taxa they include.

Clades are nested within one another, with smaller clades encompassed by larger ones. For example, the human species forms a clade that is a single branch within the larger clade of the hominin lineage, which is a single branch within the larger clade of the primate lineage, which is a single branch within the larger clade of the mammalian lineage, and so on, back to the most encompassing clade of all: the entire tree of life.