Organic compounds formed by addition of alcohol molecules to aldehyde molecules. If one molecule of aldehyde (RCHO) reacts with one molecule of alcohol (R1OH) a hemiacetal is formed (RCH(OH)OR1). The rings of aldose sugars are hemiacetals. Further reaction with a second alcohol molecule produces a full acetal (RCH(OR1)2). It is common to refer to both types of compound simply as ‘acetals’. The formation of acetals is reversible; acetals can be hydrolysed back to aldehydes in acidic solutions. In synthetic organic chemistry aldehyde groups are often converted into acetal groups to protect them before performing other reactions on different groups in the molecule. See also ketals.
http://www.acdlabs.com/iupac/nomenclature/93/r93_460.htm Information about IUPAC nomenclature