Despite its name, the posterior pituitary gland is not a gland, per se; rather, it is largely a collection of axonal projections from the hypothalamus that terminate behind the anterior pituitary gland.
Classification of the posterior pituitary varies, but most sources include the three regions below:
pars nervosa, or neural lobe, or posterior lobe
This region consistutes the majority of the posterior pituitary, and is sometimes (incorrectly) considered synonymous with it. Notable features include Herring bodies and pituicytes. 
Also known as the "infundibulum" or "pituitary stalk". The term "hypothalamic-hypophyseal tract" is a near-synonym, describing the connection rather than the structure.
This is only occasionally included as part of the posterior pituitary. Other sources specifically exclude it from the pituitary.
A few sources include the pars intermedia as part of the posterior lobe, but this is a minority view.
Major hormones secreted
Hormones known classically as posterior pituitary hormones are synthesized by the hypothalamus. They are then stored and secreted by the posterior pituitary into the bloodstream.