## 1 Introduction  
If the Web 2.0 (or Social Web) is a \"fact\", the Web 3.0 (or Semantic Web) is a rather clear conceptual model that experiments with certain difficulties deployed and applied in practice environments. Looking at the state of the art and the evolution of the last few years, there is a constant feeling of a technological and probably also conceptual gap between the Web 2.0 and Web 3.0. On one hand, there is the need to provide a new generation of Social Web focused on the social/community intelligence. On the other hand, there exists a set of semantic technologies that, at the moment, appear difficult to be applicable for generic purposes (Semantic Web) but that could propose extreme effectiveness in specific contexts (in this case, Social Semantics). That gap motivates the formalization of a middle concept between the Web 2.0 and the Web 3.0. For the meaning the concept has and the \"role\" that it is assuming, this concept is naturally understood and referred to as Web 2.5. Even if most researchers agree that Web 2.5 should be defined according to the real evolution of the web, a formal definition reflecting a common understanding is not yet available. The nature, the role and the understanding of Web 2.5 is represented in Figure 1, where the theoretical evolution of the Web (in decades) is compared with the real evolution. As showed, the socialization is related to the application of semantics. The linear relation between them (as represented in the Figure 1) is just theoretical. The first decade of the computer (1980-1990) is commonly understood as the PC era (Figure 1), where the computation normally matches the \"Desktop vision\" that assumes individual computers have a strongly limited degree of co-operation. Figure 1: Theoretical _vs._ real Web evolution. The need for networking progressively addresses the first version of the Web and of the development of related technologies (web technologies). The Web 1.0 is also referred as syntactic web and it is associated with the decade between 1990-2000. In this period, the World Wide Web vision progressively replaces the Desktop vision. The second version of the Web (Social Web or Web 2.0) is related to the decade between 2000-2010. The strong socialization of the Web is clearly proven [1]: improved multimedia capabilities [2, 3] as well as content sharing facilities [4] provided by broadband are a fact that determined not only web applications but also Rich Internet Applications [5].According to the theoretical evolution of the Web (Figure 1), the third decade should provide the thorough application of semantics [6], although considering the strong advances of the last generation of semantic technologies, there is an objective delay. On the other hand, during the past few years, virtualization techniques (e.g., [7]), cloud vision [8] and above all, mobile computing [9] alongside the increasing use of smart devices, provides interesting new scenarios. These scenarios, both with the latest advancement in the development of semantic technologies, are converging on the Web 2.5 concept to address a model of the Web beyond the social (Web 2.0) but not yet semantic (Web 3.0). If the analysis in Figure 1 is focused just on the relation between socialization and semantics, according to the forecasts, it should have been evolving in accordance with a linear relation. The facts are highlighting socialization as a faster process than the affirmation of semantics. This non linear relation produced the Web 2.5 and not (yet) the Web 3.0. This paper presents a formalization of the Web 2.5, based on the most natural understanding: the convergence between the socialization of the web and semantic technologies [10, 11, 12, 13]. The first part of the paper shortly discusses the Web 2.0 and the Web 3.0 as well as the technological (and probably also conceptual) gap between them. The key models are lightly formalized by using concept maps.