Legal definition: A complaint is a formal statement to a government authority that you have a legal cause to complain about the way you have been treated.
This term “complaint” can be translated with different meanings based on the context.
Today, an example was brought for learning purposes.
As you can see on the image, “complainant” and “complaint” were translated different. The translations were correct; however, there is a slight difference on the meaning of “denunciante” and “demandante”.
* Reasoning: The difference is the legal field: “denuncia” (penal) and “demanda” (civil).