Basal is a term used in phylogenetics (for an introduction, check out our article on parsimony). A clade is a a group comprising one extinct, or extant, species and all its descendants. A basal clade, is the earliest branching clade in a larger clade. For exampls, the family Homininae (the great apes) is a clade consisting gorillas, humans, bonobos and chimpanzees. Humans, bonobos and chimpanzees share a more common ancestor, than they do with gorillas; the gorillas are the earliest branching group in the Homininae, and so are the basal clade.