A messiah was an individual who had the power to save a people group or members of a religion from some calamity.
In 2373, Q proposed that he and Kathryn Janeway have a child together, saying the Q Continuum needed a new messiah. (VOY: "The Q and the Grey")
In 2377, after learning that his daughter could be the prophesied kuvah'magh, Tom Paris remarked to B'Elanna Torres, " I was hoping our daughter would be special, but I never dreamed she'd turn out to be the Klingon messiah." Torres didn't appreciate his comments, fearing the child's life might be in danger. (VOY: "Prophecy")
In the final revised draft of the script for "The Conscience of the King", Kodos (according to Kirk) appointed himself as a Messiah before flipping the switch that killed the four thousand Tarsus IV colonists.