A clade is a monophyletic taxon or monophyletic group if you prefer. A monophyletic taxon (or a clade) is defined as a taxon that contains only all descendants of a common ancestor and the common ancestor.
A taxon (Plur. taxa) is any (monophyletic or not) group of species. For example the group of yellow flowers is a taxon. The group of primates is a taxon. The taxon of aquatic animals is a taxon. A clade is a monophyletic taxon or monophyletic group if you prefer. A monophyletic taxon (or a clade) is defined as a taxon that contains only all descendants of a common ancestor and the common ancestor. On the following picture, only the Taxon 1 is a clade. To cite few examples of clades: Primates, Eukaryotes, Rosacea, Reptilomorpha, Rodentia. (The links yield to tolweb.org. Evolutionary trees depict clades. A clade is a group of organisms that includes an ancestor and all descendants of that ancestor. You can think of a clade as a branch on the tree of life. Some examples of clades are shown on the tree below. Phylogenetic systematics, a.k.a. evolutionary trees : Reading trees: A quick review. A phylogeny, or evolutionary tree, represents the evolutionary relationships among a set of organisms or groups of organisms, called taxa (singular: taxon). Branches and clades • Evolutionary trees depict clades. •A clade is a group of an ancestor and all descendants.•You can think of a clade as a branch of the tree of life. •Some examples of clades and non-clades in a phylogenetic tree are shown here.
http://biology.stackexchange.com/questions/17590/what-is-the-difference-between-these-terms-clade-monophyletic-group-and-taxon http://evolution.berkeley.edu/evolibrary/article/phylogenetics_02 http://evolution.berkeley.edu/evolibrary/article/phylogenetics_02 http://www.calvin.edu/~rpruim/talks/SC11/2011-06/SC11-Calvin-Rendon/bioinformatics.Day2/D2.1.Reading%20Phylogenetic%20Trees.pdf
What is the relationship between a clade and a taxon?