In the last years the user information seeking process on the Web has shifted from document search to object search. Hence, the answers provided by Web search engines cannot consist any more in a mere list of pages. In this paper we consider queries returning mono-, ambiguous, or multi-domain results, where the domain represents a specific field of interests such as City, People, Movies, etc. and we characterize the problem for the definition of the layout of such results. In particular, we describe a conceptual definition of the Web search result layout problem, by identifying: the parameters involved in the layout design, the tuning dimensions available for optimizing the result layout, and the possible strategies that can be adopted for producing such layouts. Finally, we provide an outlook on the possible future research directions on this topic.