Organic compounds, similar to acetals, formed by addition of an alcohol to a ketone. If one molecule of ketone (RR′CO) reacts with one molecule of alcohol R′OH, then a hemiketal is formed. The rings of ketose sugars are hemiketals. Further reaction produces a full ketal (RR′C(OR′)2).
http://www.acdlabs.com/iupac/nomenclature/93/r93_460.htm Information about IUPAC nomenclature