What term should be used for a written expression of dissatisfaction?

The term "complaint" is correctly identified as the written expression of dissatisfaction. In a formal context, such as in healthcare or customer service, a complaint refers specifically to a documented expression that outlines the issues or grievances a person has regarding a service, product, or treatment received. This term is widely used in professional and legal contexts, where it serves to convey the details of the dissatisfaction in an official manner, often requiring a response or resolution.

The other terms do not fit this context as precisely. "Complain" is a verb that refers to the act of expressing dissatisfaction but does not indicate that it is written. "Complainant" refers to the individual who is voicing the complaint and does not encompass the nature of the written grievance itself. Similarly, "complainant's statement" implies a broader context and may not strictly refer to a written expression of dissatisfaction, as it could encompass verbal or informal remarks by the complainant. Therefore, "complaint" is the most accurate term for a written expression of dissatisfaction.