Security is a very active field, were too much terminology is vaguely defined. This leads to difficulties for applications to evaluate their security level in order to communicate in safety manner. This problem increases when these applications use mobile agents. Indeed, mobile agents have to estimate the trust of environment where they will be executed. This issue is addressed, in this paper, by the use of security ontology. The development of this ontology must follow a process which consists on a set of phases in order to leads to a typical ontology.