What is a chordata?
A class of organisms much like fish , frogs,reptiles, birds, mammals which have similarities in body plan.
First understand the word: phylum
Think of it as grouping based on similarity an organisms body plan.
So now we have phylum Chordata: Chordata type of body plan during their life cycle.
Features of chordata include: something like a spine, gills as in a fish, a post anal tail,.