Capping is short for frequency capping in digital marketing and advertising contexts.
Capping consists in specifying a maximum number of displays from a single visitor identified by a cookie at the setting on line phase of an advertising campaign with an ad server. The goals of capping are to optimize campaign ROI and to prevent user annoyance and irritation.
A capping threshold of 5 to 7 days means that the same individual will theoretically only see 5 times a banner over the same period.
To intrusive formats like some transparent flash on the homepage, the campaign is often capped to 1. This means that the visitor will only see once the creation, even if he comes back or refresh the page. He/she may see it again with a "see again" click opportunity often proposed or by deleting the cookie.
Capping is also used as part of retargeting to avoid an effect of harassment or other elements that are not necessarily ad creatives (newsletter lightbox subscription, solicitation for a poll on a website, etc.)
Capping can be specified on a time period or per visit session, it is called daily capping or session capping.
Possibility of capping an advertising campaign results generally in a CPM increase of about 10 to 15%.