The term "repudiation" is indeed often used to mean a repudiating statement or action that constitutes a material breach.
Note: Not every repudiating statement or action constitutes a material breach at the time of the statement or action. To avoid confusion, recall what a repudiating statement or action is. A repudiating statement is a statement that one will--in the future--materially breach by non-performance.
A repudiating action is a voluntary action that means one will--in the future--materially breach by non-performance. The question is when a statement or action about a future material breach by non-performance is itself enough to count as a material breach at the time of the statement or action. We turn to the rules that answer this question.