An object in a given data set is a contextual outlier (or conditional outlier) if it deviates significantly with respect to a specific context of the object (Section 12.1). The context is defined using contextual attributes. These depend heavily on the application, and are often provided by users as part of the contextual outlier detection task. Contextual attributes can include spatial attributes, time, network locations, and sophisticated structured attributes. In addition, behavioral attributes define characteristics of the object, and are used to evaluate whether the object is an outlier in the context to which it belongs.