Starting areas are where players begin the game in World of Warcraft as level one characters, based on their selection of race. Players are more or less free to travel wherever they want from the starting location, but it is generally recommended that one complete the character — and race-specific — quests in and around the character's starting location.
All starting areas have one small village, outpost, or town with trainers for all classes and are available to the race(s) that controls the area. There are no profession trainers or inns in starting areas; however, when a starting player first uses his Hearthstone, he is teleported back to the main settlement in the area. Once the player changes where his hearthstone is set, he cannot change it back to the starting area. The second expansion features a new zone where death knights start in. New Death Knights do not actually begin in the Eastern Plaguelands, instead, they begin in an instance which strongly resembles the Eastern Plaguelands.
Though all starting areas are protected by level 65 guards, there is no real need for them, as quest givers in starting areas are not flagged for PvP and may not be killed by enemy players, even on PvP servers. This is likely intentionally done by Blizzard to prevent enemy players from killing beginning quest givers and preventing new characters from playing the game.
See Starting areas category for a list of player starting areas.