This is an Apple UK plug, so if you need a spare plug or you are coming to the UK, then this plug will simply fit onto your MacBook ac adapter and allow you to plug into the UK power outlet or any country that uses the standard UK power sockets.
Connection: 2 hole snap on plug (also known as the Duckhead adapter)
Country electric socket type: UK
Contents: Apple UK 3 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 US and European version which are shown below.