Opportunity to see
Opportunity to see is a term which refers to an advertising campaign and the number of exposures or opportunities which a particular audience has to see a specific advert. In context of radio advertising, the applicable relevant term is opportunity to hear.
For example, OTS coverage of 40% means that 40% of the target audience saw the advertisement.
OTS has been a traditional metric determining advertising value, through in the Internet era it is also supplemented by the pay-per-click metric.