Combining Diacritical Marks is a Unicode block containing the most common combining characters. It also contains the Combining Grapheme Joiner, which prevents canonical reordering of combining characters, and despite the name, actually separates characters that would otherwise be considered a single grapheme in a given context.
In digital typography, combining characters are characters that are intended to modify other characters. The most common combining characters in the Latin script are the combining diacritical marks (including combining accents).