I assume you're referring to the "Mail, Contacts, Calendars" setting in "Settings." If so, the "fetch" setting tells the iPad's app (e.g. email) to "fetch" new data (e.g. mail messages) from the source when you open the app. If you set the setting to "push," the iPad opens an app in the background (according to the schedule you set) that receives the data from the source. You may enable the iPad to "notify" you when that happens, as well. Such "notification" doesn't make sense in the "fetch" mode because presumably you're looking at the screen when the app "fetches" the data.