Illustrated Glossary of Organic Chemistry

Alpha-anomer (α-anomer): A carbohydrate in which the group bonded to the anomeric carbon is trans to the CH2O group on the other side of the pyranose or furanose ring ether oxygen atom.

In α-D-glucopyranose the anomeric OH is trans to the CH2OH.   
In β-D-glucopyranose the anomeric OH is cis to the CH2OH.

Molecular structure of maltose, an α-disaccharide.   
Molecular structure of lactose, a β-disaccharide.