In a vascular plant, the stele is the central part of the root or stem containing the tissues derived from the procambium. These include vascular tissue, in some cases ground tissue (pith) and a pericycle, which, if present, defines the outermost boundary of the stele. In other words, vascular bundle or the stele consists of three tissues: the pericycle, the xylem, and the phloem.
Outside the stele lies the endodermis, which is the innermost cell layer of the cortex.
Below you will find a useful outline if various stele types.
Big thanks to http://bpp.oregonstate.edu/files/bpp/webfm/pdf/bot313/Lecture 11, Stele types.pdf and http://bpp.oregonstate.edu/files/bpp/webfm/pdf/bot313/Lecture%2011,%20Stele%20types.pdf.