I'm reading CLRS and studying the B-Tree now.
CLRS claims that B-Tree naming is not clear yet: [Bayer, McCreight, 1972] doesn't offer the reason why B-Tree is named "B-Tree".
I haven't investigated this issue any further... but does anyone know the reason? :)
This seems to be the closest I can find to an answer:
The origin of "B-tree" has never been explained by the authors. As we shall see, "balanced," "broad," or "bushy" might apply. Others suggest that the "B" stands for Boeing. Because of his contributions, however, it seems appropriate to think of B-trees as "Bayer"-trees.