Which of the following letters has a counter?

The letter that has a counter, which is defined as a fully enclosed area within a letterform, is indeed the letter g. In typography, the lowercase "g" features an enclosed space created by its loop, making it a classic example of a letter with a counter. This enclosed area is significant in calligraphy and type design, as it contributes to the character's overall appearance and readability.

The other letters do not have a counter. The lowercase "a" has a partially enclosed space but does not fully enclose a counter. The letter "b" has an enclosed area but is usually not classified as having a counter because it does not have the same characteristics as those found in fully enclosed letters. The letter "m" also lacks any fully enclosed sections. Understanding such details enhances appreciation for letterforms in calligraphy and typography.