I know what major (2.2 nm) and minor (1.2 nm) groves are, but what is then name for:
a 360-degree rotation of DNA (3.4 nm)
the gap between each base pair (0.34 nm)?
The term for distance covered in a 360° rotation of helix is known as the pitch of DNA helix, though there is no special name for distance covered between 2 base pairs. It can be called as rise per base pair of DNA. See the table below from this article:
Reference: Nucleic Acid Double Helix
It turns out that the gap between (heterocyclic nitrogenous) base pairs is called 'adjacent base pair width'. Also, the pitch (10 base pairs long) is also known as 'one helical turn'. Just a bit of additional information...