In terms of marketing and advertising, AOR means agency of record. Agency of record means one company hired another company, usually in the marketing/advertising industry, to handle the marketing and promotion of an advertising campaign of some sort. It can vary from company to company, depending on the service being rendered, but mostly, it is that.
An example of what an AOR is in online marketing would be an affiliate network offering an offer that is exclusive to that network. Basically, the one company contacts the network and gives them favorable terms in order to run their campaign exclusivley, This is usually a win-win situation for the network and the advertiser. The network gets to advertise it as exclusive and doesn’t have to worry about affiliates moving from that network to another network for that offer. The advertiser knows what company is screening the affiliates, so fraud is less of a concern as well.
An AOR can also outsource or just be one person looking to get affiliates to a program. If a network allows brokering of their offers, they could be the AOR of an offer and make other companies come to them in order to run the offer. That is a huge benefit to the AOR, as all traffic and sales will first go through the company.
So basically, an AOR is the middleman between a company and affiliates (and sometimes other networks) who is in charge of handling the entire marketing and advertising portion of the business.