Short answers, pulled from the story.
Munera (singular munus) is a Latin word meaning "duty" or "obligation," related to the English word "munificence." In ancient Rome it referred to public works and entertainments provided by wealthy individuals for the benefit of the Roman people, and it was often used as a synonym for gladiatorial combat.
Munera depended on the private largesse of individual wealthy Romans, while ludi were games, athletic contests, or spectacles sponsored by the Roman state. The distinction placed munera in the realm of personal generosity and civic obligation rather than official public expenditure.
Gladiatorial contests began as funeral tributes sponsored at the tombs of deceased Roman magnates by their heirs. The combat was a service or gift rendered to honor the dead, not initially a form of mass public entertainment.
From the time of the Tetrarchy (293-305), the Roman state began regulating and enforcing what city councilors called curiales were required to provide. Before that shift, the crises of the Empire after 235 caused a dramatic decline in voluntary private expenditure, visible in the drop in inscriptions crediting private donors with building works.
Munera sordida, meaning "dirty" works, were compulsory physical labor obligations imposed on lower-status Romans. They included tasks such as making charcoal, lime-burning, and breadmaking, as well as corvee labor in state factories, mines, quarries, and on public buildings and roads.
Wealthy Romans tried to escape compulsory munera primarily by rising to senatorial rank or by obtaining imperial grants of exemption. Those who succeeded, particularly the richest city councilors called principales, shifted their burdens onto less wealthy colleagues, which weakened municipal government across the Empire.