Simple Definition:

A kleptocracy is a type of government where the ruling class [the group of people in power] steals or misuses public funds [money owned or controlled by the government and used for the benefit of the people] for personal gain.

For example, in a kleptocracy, government officials may embezzle [to steal money from the place where you work] money meant for infrastructure projects [large-scale construction projects that improve public facilities such as roads, bridges, and schools] and use it to buy luxury items for themselves.

Very Simple Definition:

A kleptocracy is when the people who run the government steal money that is supposed to help everybody.

For example, in a kleptocracy, the people in charge might take money that was meant to fix roads and use it to buy expensive things for themselves.