Node Body | Modules Unraveled
Contextual Filters work the same way that Filter Criteria do, except that Contextual Filters create the filters dynamically. For example, if we were to add a filter criteria for author uid, we'd have to select one uid. If we chose "uid-1", the view would always show content by user 1 regardless of who is viewing the page. If we want to add a filter like "content created by the currently logged in user", we'll have to add a contextual filter. Let's go ahead and do just that.