Briefly explain the Missouri plan and the role played by retention election in it

What will be an ideal response?

An ideal response would be:
One of the oldest merit plans is the Missouri Plan. As used in most states, the Missouri Plan provides that when a judicial vacancy occurs, a special nominating commission nominates several candidates. The governor selects one, who then serves as a judge for at least a year. At the next general election, the judge runs in a noncompetitive retention election where the voters are asked to vote yes or no on whether the judge should be retained in office. If a majority of the voters agree, the judge serves a new full term (typically 6 to 12 years); if not, another person is selected by the same procedure. Some retention elections require a supermajority vote. States now use all kinds of variations on this original plan.