Recall the definition of anomers

In cyclic forms of glucose, the aldehyde group at $C-1$ reacts with the hydroxyl group to form a hemiacetal. This creates a new chiral center at carbon 1, called the anomeric carbon.

What distinguishes anomers?

Two cyclic sugar forms are called anomers if they differ only in the configuration at the anomeric carbon.

For glucose, the anomeric carbon is $C-1$.

Thus, $\alpha$-D-glucose and $\beta$-D-glucose are anomers because they differ only at $C-1$.

Evaluate the options

A: isomers of glucose that differ in configurations at carbons one and four ($C-1$ and $C-4$)

• Incorrect. Difference at both $C-1$ and $C-4$ would not define anomers.

B: a mixture of (D)-glucose and (L)-glucose

• Incorrect. $D$- and $L$-glucose are enantiomers, not anomers.

C: enantiomers of glucose

• Incorrect. Anomers are a special type of diastereomers, not enantiomers.

D: isomers of glucose that differ in configuration at carbon one ($C-1$)

• Correct. This is exactly the definition of anomers in glucose.

Final answer

The term anomers of glucose refers to isomers of glucose that differ in configuration at carbon one ($C-1$).