Feature Scope

A Feature's scope enables developers quantify how broad the effects of activating the Feature are. If a Feature is scoped at the site level, then activation affects only the SharePoint site it is activated within. However, if it is scoped at a site collection level, then the activation affects all sites within the site collection. To administrator, the scope affect where the feature can be activated to after the feature is installed. If it is farm feature, it can be activated at http://.../_admin/ManageFarmFeatures.aspx, if it is webApplication feature, it can be activated at http://.../_admin/ManageWebAppFeatures.aspx, if it is sitecollection, it can be activated at http://../sitecollection/_layouts/ManageFeatures.aspx?Scope=Site, if it is site feature, it can be activated at http://../site/_layouts/ManageFeatures.aspx

To a developer, the scope affect the receiver's properties.Feature.Parent. For example, if it s a web feature. You can write code like, SPWeb site = properties.Feature.Parent as SPWeb;