A multicellular organism is a living organism that is made up of multiple cells. The term "multicellular" is often used to describe organisms that are composed of more than one cell. This category includes trees, plants, animals, and humans. Many synonyms can be used to describe multicellular organisms. Some of these synonyms include "complex organisms," "pluricellular organisms," "metazoans," "multi-celled organisms," and "colonial organisms." These synonyms reflect the diverse nature of multicellular organisms and the many different ways in which they are classified and studied. Regardless of the term used, however, all multicellular organisms share the common trait of being composed of multiple cells, each with its own specialized function.