In the web world, "attribution" is generally used to describe the originating source of a web page visit. For example, if you search on Google and then navigate to a given search result, you will be attributed to a Google search. If, on a later visit, you arrive at the destination web page via an advertisement, that will be attributed to the advertisement you clicked. In short, a given user with multiple visits may be attributed to multiple sources.
In the mobile world, however, "attribution" is generally used to describe the originating source of an installation. By design, Localytics does not attribute a given user to more than one originating source. This allows you to measure downstream metrics, like lifetime value, while splitting or filtering by acquisition source.