In the braille alphabet, what do each letter represent?

In the braille alphabet, each letter is represented by a combination of raised dots arranged in a grid pattern within a cell. Each cell can contain up to six dots arranged in two columns of three dots. The specific arrangement and presence of these dots correspond to individual letters, numbers, or punctuation marks. Therefore, "dots" is the correct terminology to describe these raised features that form the braille characters.

The term "bumps" while somewhat descriptive, does not accurately capture the precise nature of braille, which is specifically designed using dots for the purpose of readability and distinctiveness. Other options like "lines" and "shapes" do not appropriately reflect the fundamental structure of braille, as the system is not based on linear forms or arbitrary shapes, but rather specific dot patterns that serve a defined linguistic function. Thus, "dots" correctly identifies the basis of the braille system.