CPARS is where the government formally rates how you performed on a contract, on measures like quality, schedule, and management, using a scale that runs roughly from exceptional down to unsatisfactory. Those ratings follow you: they show up as past performance information that evaluators on future, unrelated competitions can pull and read. You usually get a chance to comment on a rating before it is finalized, which is worth doing, since a rating you disagree with and never responded to is much harder to argue with later.

In a sentence

"Your firm's CPARS rating on the prior task order was Satisfactory across all evaluated areas." That rating is not just a courtesy note, it becomes part of your permanent record that shows up when you compete for completely different work down the road.