= Glycosyl group
A <glycosyl group> is a substituent obtained formally by removing the <hydroxy group> at the <anomeric carbon> of a cyclic <monosaccharide>. The resulting attachment site connects that sugar-derived unit to another part of a <molecule>. Removing the whole <hydroxy group> differs from removing only its hydrogen: the latter leaves an oxygen at the attachment site.<Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 by IUPAC>[P-102.6.1.1.1, Glycosyl groups]{ref}
For an atom-count example, cyclic <glucose> has <molecular formula> $\mathrm{C_6H_{12}O_6}$. Subtracting an anomeric $\mathrm{OH}$ gives a <glycosyl group> fragment with composition $\mathrm{C_6H_{11}O_5}$. Attaching that fragment to $\mathrm{OCH_3}$ gives $\mathrm{C_7H_{14}O_6}$. The oxygen joining the sugar-derived group to the <methyl group> belongs to the attached $\mathrm{OCH_3}$ fragment in this bookkeeping. The formal subtraction describes connectivity, rather than prescribing a preparative reaction.
A name also needs the ring form and, when specified, the <anomer> configuration. Thus the glycosyl naming rules retain information about the cyclic sugar and its attachment; a <molecular formula> alone does not distinguish all such structures. <Glycosyl groups> occur in names of <glycosides> and <oligosaccharides>, connecting <functional group> nomenclature with <glycosidic bonds>.<Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 by IUPAC>[P-102.6.1.1–P-102.6.1.2, glycosyl substituents and O-glycosyl compounds]{ref}
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