The story
From H + DNA. From containing Hoogsteen-type nucleobase bonding, in addition to Watson-Crick normal style bonding of base pairs.
Etymology from Wiktionary, CC BY-SA 4.0.
H-DNA
Today it means: A configuration of DNA, a triple-stranded DNA helix structure, right-hand twisting, where the third DNA strand fills in the major groove found in B-DNA, bonding to the B-DNA with Hoogsteen-type bonding, forming Hoogsteen base pairs. Full definition →