The Free On-line Dictionary of Computing (30 December 2018):

B-tree

    A multi-way balanced tree.

   The "B" in B-tree has never been officially defined.  It could
   stand for "balanced" or "Bayer", after one of the original
   designers of the algorithms and structure.  A B-tree is _not_
   (necessarily?) a "binary tree".

   A B+-tree (as used by IBM's VSAM) is a B-tree where the
   leaves are also linked sequentially, thus allowing both fast
   random access and sequential access to data.

   [Knuth's Art of Computer Programming].

   [Example algorithm?]

   (2000-01-10)