Ad serving describes the technology and service that places advertisements on web sites. Ad serving technology companies provide software to web sites and advertisers to serve ads, count them, choose the ads that will make the web site or advertiser most money, and monitor progress of different advertising campaigns.
Two types of internet companies use ad serving: web sites and advertisers. The main purpose of using an ad server is different for both of them:
For a web site, the ad server needs to look through all the ads available to serve to a user who is on a page, and choose the one that will make the web site the most money, but still conform to the rules that the advertiser and web site have agreed. For example if a web site has 10 different advertisers that have paid for a big square ad, the ad server must decide which one to serve (or display). One advertiser may have only agreed to pay for ads from 9am – 5pm. If it is after 5pm, then the Ad Server must not serve that one. Another advertiser may only have paid to show one ad to each user per day. The ad server must therefore see if a user has seen that ad before, on that day and not serve it again if the user has seen it. Another advertiser may have agreed a high price, but only if the person watching the page is in the United States. In that case, the Ad Server needs to check the IP address to determine if the user is in the US and then decide which is the highest paying ad for that user, in the US, at that time, given what that user has seen in the past.
For an advertiser the ad server needs to try to serve the ad that is most likely to result in a sale of the product advertised. For example if a user is viewing a page, the advertiser’s ad server needs to decide from previous history, what ad that user is most likely to click on and then buy the product advertised. If the user is on a technology page, then the ad server may know that on technology types of pages, the ad that works best is a blue one with mostly text and pricing and numbers, not the green ad with a picture of a model and little text. The ad server will therefore serve this ad, to try and get the highest probability of a sale from the ad.
Ad Serving is most complex when it is used by an Advertising Network. An advertising network buys ads from many web sites and therefore acts like an advertiser user of Ad Serving. When the network buys ads, it tries to place ads on sites where they work best. However an ad network then sells its aggregated ad inventory to advertisers. When doing this, it uses its Ad Serving software as a web site does. In this case it tries to make the most money by only running the ads from advertisers that pay most.