What are animals? what is the definition of Animalia?
Any of numerous multicellular eukaryotic organisms of the kingdom Metazoa (or Animalia) that ingest food rather than manufacturing it themselves and are usually able to move about during at least part of their life cycle. Sponges, jellyfishes, flatworms, mollusks, arthropods, and vertebrates are animals.
or…
Any member of the kingdom Animalia, comprising multicellular organisms that have a well-defined shape and usually limited growth, can move voluntarily, actively acquire food and digest it internally, and have sensory and nervous systems that allow them to respond rapidly to stimuli: some classification schemes also include protozoa and certain other single-celled eukaryotes that have motility and animal-like nutritional modes.