1.Technically, taxonomy terms are an entity type and the entity subtypes are the vocabularies.
2. Individual taxonomy items are known as terms (the blog tags or recipe ingredients in these examples); and
a set of terms is known as a vocabulary (the set of all blog post tags, or the set of all recipe ingredients in these examples).
==> a term = a taxonomy item
=> Vocabulary = basket( term1 + term2 + ... + termi )
先有term后有vocabulary
