Short answers, pulled from the story.
Constitutional monarchy is a form of government in which the monarch exercises authority within limits set by a constitution, rather than ruling alone. Unlike absolute monarchies, constitutional monarchies require the ruler to share decision-making power and operate within an established legal framework.
The Hittites of ancient Anatolia had the oldest known constitutional monarchy. Their Bronze Age king was required to share authority with an assembly called the Panku, whose members came from noble families and acted as representatives of their subjects.
Queen Anne was the last British monarch to veto an Act of Parliament, blocking the Scottish Militia Bill on the 11th of March 1708. No monarch has exercised that power since, and it is widely regarded as a lapsed power.
On the 11th of November 1975, Governor-General John Kerr dismissed Prime Minister Gough Whitlam after the Australian Senate threatened to block the government's budget. Kerr installed opposition leader Malcolm Fraser, who secured passage of the appropriation bills and won a subsequent double dissolution election with a large majority.
In executive constitutional monarchies, also called semi-constitutional monarchies, the monarch retains significant powers such as appointing and dismissing ministers and dissolving the assembly. In ceremonial constitutional monarchies, the monarch holds little direct political power and serves primarily as a symbolic head of state.
There are currently 43 monarchies worldwide operating under some form of constitutional arrangement. Slightly more than a quarter are in Western Europe, while the two most populous constitutional monarchies, Japan and Thailand, are in Asia.