"Costume packs" refers to sets or collections of costumes or outfits that can be purchased together, often for use in a video game, play, or costume party. Full definition
There's also plans for added DLC costume packs to be released later on for a dollar a piece, but those will be released at a later time. (gamerassaultweekly.com)
As far, the downloadable content has been somewhat underwhelming, focusing largely on costume packs as well as small free updates. (playiplay.com)
If you are a fan and want to unlock the upcoming characters or alternate costume packs, the final package becomes a very expensive proposition. (gameondaily.com)