Illustrated Glossary of Organic Chemistry

D: (1) A carbohydrate that has the same stereocenter absolute configuration at the second-to-last carbon in its chain (in acyclic form) as (R)-glyceraldehyde (also called D-glyceraldehyde). Note that when 'D' is used to denote carbohydrate relative configuration, it is of a smaller font than the name of the carbohydrate.
D-Glyceraldehyde             D-Glucose

(2) The chemical symbol for 2H, the hydrogen isotope called deuterium. For example, D-Cl is 2H-Cl.