The term phylum is one of the seven major classification groups that biologists use to identify and categorize living things. These seven groups are hierarchical or range in order of size. Phylum is the second largest and is located between kingdom and class. The classification scheme for all living things is: kingdom, phylum, class, order, family, genus, and species.
The category phylum is fairly broad, and members of the same phylum can be very different and have only basic similarities. Organisms in the same phylum, however, are presumed to have a common evolutionary ancestry. To determine an organism's place in a particular phylum, biologists study it to find similarities and differences between it and other organisms within the kingdom. An example within the animal kingdom is Chordata, which contains all vertebrates (animals with a backbone). Fish, amphibians, reptiles, birds, and mammals all belong to the phylum Chordata. However, invertebrates (no backbone) of the animal kingdom, like snails, clams, and octopus, belong to the phylum Mollusca. Others, like insects and crabs, belong to the phylum Arthropoda. The animal kingdom can be divided into twenty or more phyla.
Within the plant kingdom, the term "division" is used instead of phylum. Examples of some divisions include Coniferophyta (cone-bearing plants such as pine trees) and Anthophyta (plants that have flowers able to develop into seeds). Altogether, there are ten divisions (or phyla) in the plant kingdom.
phy·lum / ˈfīləm/ • n. (pl. -la / -lə/ ) Zool. a principal taxonomic category that ranks above class and below kingdom. ∎ Linguistics a group of languages related to each other less closely than those forming a family, esp. one in which the relationships are disputed or unclear.