The title in French is 'L'Hote', which means both the 'The Guest' and 'The Host'. How does this ambiguity reflect on the story?
In many ways, this story is both about the guest and the host. Readers are drawn to the struggle of Daru to keep a man imprisoned that he feels should be released. They are also drawn to the struggle of the Arab and the confusion as to why the Arab committed the act of violence he is accused off. In addition, Algeria was "host" to the French - the invading force - and yet the French take over the role of host and treat the Algerians as guests, visitors in their own country.
Besides these paradoxes, ambiguity plays a more general role in the story. Daru is ambiguous and uncommittal about the war that is to happen. He sympathizes with the Arabs, and feels no overwhelming patriotism to the French. He does not war to happen because he does not want to have to choose sides. Furthermore, the unclear nature of the Arabs violence lends ambiguity to the story. Not only does Camus withhold details from us, but the Arab himself gives an answer that provides no answer: "He ran away. I ran after him." Daru and the readers both are still asking "why?"