Leader of the Opposition
The Leader of the Opposition, is a recognised (and often salaried) post in the Westminster System of parliamentary government. It is held by the leader of the largest opposition party (ie party not in government), and he or she also leads the Shadow Cabinet.
The role of Leader of the Opposition is similar in some ways to that of a minority leader in a legislative body, but also serves as a challenger to the prime minister at the next general election.
In the British parliament, the current Leader of the Opposition is the Conservative Party leader, David Cameron. His full title is Leader of Her Majesty's Loyal Opposition, indicating that whilst opposition politicians may disagree with the government of the day, they are expected to be loyal to the monarch and by extension Britain itself.
In Australia, there is a leader of the opposition at the federal level and also in each state and territory. The current leader of the opposition at the federal level is the leader of the Liberal Party, Malcolm Turnbull.