This is an Apple US plug, so if you need a spare plug or you are going to the US, then this plug will simply fit onto your MacBook ac adapter and allow you to plug into the US power outlet or any country that uses the standard US power sockets.
Connection: 2 hole snap on plug (also known as the Duckhead adapter)
Country electric socket type: US (USA)
Contents: Apple US 2 pin plug
Compatible with: Any Apple MacBook, MacBook Pro, MacBook Air, IPod, Ipad, Iphone, basically any Apple device that has a two hole connector lead or plug that can be removed.
Also available are the UK and European version which are shown below.