In order to determine the reach of a given online platform or online search engine, it is necessary to establish the average number of active recipients of each service individually. Accordingly, the number of average monthly active recipients of an online platform should reflect all the recipients actually engaging with the service at least once in a given period of time, by being exposed to information disseminated on the online interface of the online platform, such as viewing it or listening to it, or by providing information, such as traders on an online platforms allowing consumers to conclude distance contracts with traders. For the purposes of this Regulation, engagement is not limited to interacting with information by clicking on, commenting, linking, sharing, purchasing or carrying out transactions on an online platform. Consequently, the concept of active recipient of the service does not necessarily coincide with that of a registered user of a service. As regards online search engines, the concept of active recipients of the service should cover those who view information on their online interface, but not, for example, the owners of the websites indexed by an online search engine, as they do not actively engage with the service. The number of active recipients of a service should include all unique recipients of the service that engage with the specific service. To this effect, a recipient of the service that uses different online interfaces, such as websites or applications, including where the services are accessed through different uniform resource locators (URLs) or domain names, should, where possible, be counted only once.