A growing interest for pervasive applications and an increasing diversity of pervasive computing devices integrated in our surroundings demand incorporating context-awareness in such applications in order to protect users from being disturbed by such services while on their regular duty. The behavior of these applications should depend not only on their internal state and user interactions but also on the context sensed during their execution. Context and context awareness, therefore, are the key components of pervasive computing so as to perform tasks on behalf of users. In this paper, we propose ontology based reusable context model. The model facilitates the context reasoning by providing structure for contexts, rules and their semantics. Initial prototype of the use of the model in a multi-domain platform is created and the result obtained is promising.