Dihydric alcohols, also known as diols, in which the two hydroxy groups are on different carbon atoms, usually but not necessarily adjacent. E.g.
HOCH2CH2OH 'ethylene glycol' (ethane-1,2-diol),
HO[CH2]4OH butane-1,4-diol.
Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1337 (https://doi.org/10.1351/pac199567081307)