"To have a cap" means to have a limit or a maximum amount on something. It suggests that there is a boundary or restriction on what can be done or achieved. Full definition
The vast majority of the funds raised were through the committee's «housekeeping» or soft money account that did not have caps on contributions levels. (nystateofpolitics.com)
He is not worth 20 million a season yet and we do not have the cap space currently to sign him to that type of deal. (sbnation.com)
But this card doesn't have any caps on cash back, so you earn the cash back you deserve. (creditcards.get.com)