Final answer:
In a control matrix, the coding M-1 refers to the first major control plan, which indicates a significant control activity essential for achieving control objectives.
Step-by-step explanation:
In a control matrix, the coding M-1 typically designates a major control plan. Control matrices are used to document and analyze the internal controls of a system, particularly in the context of auditing and systems design. Here, 'M' usually stands for 'Major' to indicate significant control activities that are essential for achieving control objectives, while the number generally refers to the specific identifier of that control plan within the matrix. Therefore, M-1 would be understood as the first major control plan listed in the matrix.