The word "waiver" is a noun, typically referring to the act of intentionally relinquishing or abandoning a known right, claim, or privilege or a document stating such relinquishment.
A: Correct usage - "Waiver" is correctly used to refer to a signed document that releases the organizers from responsibility.
B: Correct usage - "Waiver" refers appropriately to the exemption granted by the manager, which aligns with the word's standard usage in administrative or legal contexts.
C: Incorrect usage - "Waiver" is incorrectly used here. One does not propose a waiver to explain or articulate reforms; a better fit would be a "proposal," "amendment," or "explanation."
Thus, the correct answer is option (c).