If something is full or complete, you can describe it as plenary. When you get to be a teenager, your parents can give you plenary responsibility for your siblings when they go out. They pay pretty well to boss the kids around!
Although the adjective plenary can be used to describe anything that is full or complete, it most often describes a full meeting session, as in a political meeting or a board meeting. The school board met in a plenary session today to discuss the purchase of land for a new high school. When you got asked to be the plenary speaker at the board meeting, you made sure to put it on your resume right away.