This concept generally relates to CPM-based ad campaigns. Frequency caps basically prevent individual visitors from being shown the same ad over and over while visiting a site. This may be desirable to advertisers because:
If a line item is frequency capped, the publisher is expected to only show a certain number of impressions to each visitor over a set period of time. Examples of frequency capping may include:
Frequency capping instructions will generally be associated with a line item on an insertion order (“IO”). For example, instructions may call for “5x impressions / visitor / day.” Many ad servers, including DFP, have settings that will allow publishers to set frequency caps with minimal work. Here’s a look at how this works in DFP (this view is from within an individual line item):
Instructions for frequency capping may come as a note attached to certain line items on insertion orders (IOs). If the terms of the requested frequency capping are going to be difficult for you to meet given your available inventory, get in touch with the advertiser immediately to determine an acceptable frequency of ads.
In some instances, publishers may want to voluntarily look into frequency capping as a way to improve advertiser satisfaction by ensuring acceptable results on their campaign. If certain line items are experiencing lower click rates than you’d expect (i.e., lower than the average for your site), you may want to look into capping the frequency of ads shown to visitors. Again, this will theoretically reduce “wasting” multiple impressions on visitors who are not responsive to the advertiser’s messaging.
Finally, frequency capping of ads can be a good idea if you are running various affiliate marketing offers as part of your monetization strategy. This will ensure that visitors are exposed to a number of different affiliate offers during their time on your site, and may increase the likelihood of them completing a transaction with one of them.