An Alliance territory is any area in which Horde players playing on any server will find their PvP flags turned on. Any Horde player can be attacked by a player of the Alliance while in these zones. Unlike contested territories, it does not matter whether you are on a PvP server or not.
All Alliance capital cities are considered Alliance territory to Horde players, regardless of server type. On PvP servers, Alliance territory is extended to encompass all Alliance starting areas, as well as Loch Modan, Westfall, Bloodmyst Isle, Darkshore and the Deeprun Tram.
Horde players will see a notification on their screens when entering Alliance territory.