This paper is a contribution to formal ontology study. Some entities belong more or less to a class. In particular, some individual entities are attached to classes whereas they do not check all the properties of the class. To specify whether an individual entity belonging to a class is typical or not, we borrow the topological concepts of interior, border, closure, and exterior. We define a system of relations by adapting these topological operators. Ascale of typicality, based on topology, is introduced. It enables to define levels of typicality where individual entities are more or less typical elements of a concept.