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].