Unicode 3.2 introduces a new concept called the “grapheme cluster.” Actually, the concept isn't all that new; Unicode 3.2 merely formalizes a concept that was already out there, nailing down a more specific definition and some related character properties and giving it a new name.
A grapheme cluster is a sequence of one or more Unicode code points that should be treated as a single unit by various processes:
Text-editing software should generally allow placement of the cursor only at grapheme cluster boundaries. Clicking the mouse on a piece of text should place the insertion point at the nearest grapheme cluster boundary, and the arrow keys should move forward and back one grapheme cluster at a time.
Text-rendering software ...