$\alpha -\mathrm{D}-(+)$- glucose and $\beta -\mathrm{D}-(+)$ glucose are

Two isomers which are mirror image of each other are known as enantiomers. 

Two isomers which has different configurations around a single asymmetric carbon atoms are known as epimers. Examples are D-ribose and L-ribose.

The formation of hemiacetal in a sugar generates a asymmetrical carbon with the generation of two epimers in which $-\mathrm{OH}$ group is above or below the plane of the ring. These two epimers are frequently called anomers. The anomer with the $-\mathrm{OH}$ group above the plane of Ring is called $\beta$ anomer and the other as $a$ anomer.